The Experts below are selected from a list of 7665 Experts worldwide ranked by ideXlab platform
Yohannes L Yaphary - One of the best experts on this subject based on the ideXlab platform.
-
reduction in cement content of normal strength concrete with used engine oil ueo as chemical Admixture
Construction and Building Materials, 2020Co-Authors: Yohannes L YapharyAbstract:Abstract In this study, the coupling effects of admixing a used engine oil (UEO) and reducing the cement paste content on the properties of a normal strength concrete were investigated. Initially, various tests were performed to determine the effect of the admixed UEO on the properties (i.e. workability, air content, setting times, strengths, drying shrinkage, and freezing and thawing (F–T) durability) of the reference concrete (formed in accordance with ASTM C494). Based on the acquired knowledge regarding the aforementioned effects, the chemical-Admixture type of the UEO was evaluated. The UEO largely complies with the ASTM C494 type A Water-Reducing Admixture specifications. The admixed UEO can facilitate the production of concrete with 9.4% less cement content than that in the reference concrete, but with comparable properties. This study provides a basis for realizing a more economical and eco-friendly production of concrete by both reducing its cement content and admixing UEO.
-
reduction in cement content of normal strength concrete with used engine oil ueo as chemical Admixture
Construction and Building Materials, 2020Co-Authors: Yohannes L YapharyAbstract:Abstract In this study, the coupling effects of admixing a used engine oil (UEO) and reducing the cement paste content on the properties of a normal strength concrete were investigated. Initially, various tests were performed to determine the effect of the admixed UEO on the properties (i.e. workability, air content, setting times, strengths, drying shrinkage, and freezing and thawing (F–T) durability) of the reference concrete (formed in accordance with ASTM C494). Based on the acquired knowledge regarding the aforementioned effects, the chemical-Admixture type of the UEO was evaluated. The UEO largely complies with the ASTM C494 type A Water-Reducing Admixture specifications. The admixed UEO can facilitate the production of concrete with 9.4% less cement content than that in the reference concrete, but with comparable properties. This study provides a basis for realizing a more economical and eco-friendly production of concrete by both reducing its cement content and admixing UEO.
Xiangyong Liu - One of the best experts on this subject based on the ideXlab platform.
-
sustainable resource opportunity for cane molasses use of cane molasses as a grinding aid in the production of portland cement
Journal of Cleaner Production, 2015Co-Authors: Haoxin Li, Jianguo Wu, Guofang Zhang, Zhengwu Jiang, Long Yu, Xiaojie Yang, Xiangyong LiuAbstract:Current methods used in China have failed to recycle cane molasses in an environmentally friendly way. Meanwhile, it is an urgent concern to find a cheap alternative to the present Portland cement grinding aids. However, the available literature has several limitations in properly evaluating the feasibility of using cane molasses as a Portland cement grinding aid. Therefore, the mixture of calcium sulfate and cement clinker is interground along with it, and mixture properties such as grindability, setting time, compressive strength, water absorption, compatibility with water reducing Admixture, and hydration characteristics are systematically discussed and the mechanisms of these property variations are clarified. Besides, the economic, logistical, and environmental viability are also considered. The results show that cane molasses affects the cement grindability, setting time, compressive strength, water absorption, compatibility, hydration characteristics and microstructure, and these effects are related to its content. Moderate cane molasses delays the cement setting, but it is beneficial to the improvements of compressive strength, compatibility and microstructure. However, in addition to the fact that compressive strength is lowered, compatibility becomes poor, the later hydration is postponed and the microstructure gets loose, the scale of setting delay is also lessened when excessive cane molasses is used. The results also indicate it is logistically and economically feasible, also environmentally friendly that it is recycled as a cement grinding aid. These results are crucial to its sustainable and effective uses as well as the reuse of the waste containing similar matters. Additionally, this study also helps realize the sustainable production of cement, and also to contribute to the efforts at sustainable construction.
Rafat Siddique - One of the best experts on this subject based on the ideXlab platform.
-
Center for By-Products Utilization INFLUENCE OF FLY ASH AND CHEMICAL AdmixtureS ON THE SETTING TIME OF CEMENT PASTE AND CONCRETE Influence of Fly Ash and Chemical Admixtures on the Setting Time of Cement Paste and Concrete INFLUENCE OF FLY ASH ON SETTING
2020Co-Authors: Rafat Siddique, Tarun R Naik, Bruce W RammeAbstract:Synopsis: A recurring question about use of fly ash in concrete is dealing with setting and hardening of such mixtures with our with out chemical Admixtures. This paper presents literature review on the setting and hardening characteristics of cement paste and concrete as influenced by the inclusion of fly ash and chemical Admixtures. The paper also reports the work carried out at the University of Wisconsin-Milwaukee (UWM-CBU) on the effects of Class C fly ashes from various sources on the initial-and final-setting times of non-air-entrained and air-entrained concrete; and the effects of Class C fly ash, gypsum, and various types of chemical Admixtures (air-entraining Admixture (AEA), Water-Reducing Admixture (WRA), superplasticizer, and retarding Admixture) on the initial and final setting times of cement paste. Test results indicated that: (1) both the initial-and final-setting times were relatively unaffected at low-percentage replacement of cement with Class C fly ash, although inclusion of fly ash caused large retardation in the times of setting, up to around 60 percent cement replacement; (2) initial-and final-setting times of cement paste remained essentially the same or were slightly delayed with up to 20 percent cement replacement relative to zero percent fly ash content; beyond this range, the setting times of cement paste were accelerated. Increased rate of setting occurred at cement replacement levels of 40 percent and higher irrespective of type of chemical Admixtures used. Keywords: Air-entraining Admixture (AEA), concrete, fly ash, gypsum, high-range Water-Reducing Admixture (HRWRA), paste, retarder, time of setting, Water-Reducing Admixture. INTRODUCTION Immediately upon mixing of cement and water, various chemical reactions occur leading to formation of numerous types of hydration products. The types and amount of hydration products formed depend upon duration of hydration, water-cementitious materials ratio (W/Cm), properties of constituent materials, temperature, soluble alkalis, and mineral and chemical Admixtures. The formation of hydration products causes increase in stiffness of the cementitious matrix. This stiffening behavior of the matrix is determined by the times of initial and final setting. The initial setting of the matrix refers to the beginning of solidification for a given mixture. It is generally accepted that at this stage concrete can neither be properly re-tamped nor handled or placed. The final setting refers to the stage when the mixture attains sufficient hardness to support stress. The subsequent continuing strength gain is called hardening. Setting and hardening of cement mortar mixtures are considerably influenced by inclusion of either mineral or chemical Admixtures. Generally, the setting and hardening of mortar are delayed when ASTM Class F (low-lime) fly ash is added to it. Mortar incorporating ASTM Class C (highlime) fly ash, however, has shown either both rapid or delayed setting depending upon the properties and amount of the ash. The setting behavior can be more readily modified when gypsum and chemical Admixtures such as Water-Reducing Admixture (WRA), superplasticizer, or retarding and accelerating Admixture are used. Even air-entraining Admixture is known to slightly modify setting behavior of concrete. A knowledge of setting characteristics of concrete incorporating both mineral and chemical Admixtures is needed for efficient scheduling of concrete construction, specifically floor slabs, roadways, pavements, and other flat surfaces. Limited data exist on setting and hardening behavior of paste, mortar, and concrete containing ASTM Class C fly ash and chemical Admixtures. 3 LITERATURE REVIEW Many investigators have reported on the effects of fly ash on the times of setting of cement paste and concrete. Dodson 1 investigated the setting characteristics of concretes made with both Class C and Class F fly ashes. He reported that the setting times of concrete are mainly governed by cement content and W/Cm when all other parameters are kept equal. He further added that an increase in cement content caused a decrease in the initial-and final-setting times, whereas an increase in W/Cm increased setting times. However, in general, addition of fly ash increased the setting times. Ramakrishnan et al. 2 reported on the setting characteristics of concretes made with or without fly ash. They used one high-lime fly ash and two types of cement (ASTM Type I and Type II). They concluded that inclusion of fly ash resulted in higher initial-and final-setting times compared to the concrete without fly ash for both types of cement. Lane and Best 3 reported that fly ash generally slows the setting of concrete, although both initial and final times of setting remain within specified limits. Retardation of setting due to the inclusion fly ash may be affected by the amount, fineness, and chemical composition (particularly, carbon content) of the ash. However, the fineness of cement, the water content of the cementitious paste, and the ambient temperature usually have a much greater effect on times of setting than addition of fly ash. Replacement of 60% of cement with high-carbon fly ash by mass resulted in 200% increase in the time of final setting of control concrete mixture. . Gebler and Klieger 6 studied the times of setting of concretes containing Class F and Class C fly ashes from 10 different sources for high content mixtures. They reported that inclusion of the fly ash increased the initial-and finalsetting times of concrete mixtures. Carette and Malhotra 7 reported the setting characteristics of concretes made with fly ashes from different sources. Calcium oxide (CaO) contents of the fly ashes varied between 1 % and 13 %. They concluded that, in general, the fly ashes increased the initial-and final-setting times of concrete. Bilodeau and Malhotra 8 reported properties of concrete incorporating high volumes of Class F fly ashes from three different sources. Cementitious materials content was 300, 370 and 430 kg/m 3 , and three W/Cm (0.39, 0.31 and 0.27) were used. They concluded that for every W/Cm, the initial-and final-setting times of high-volume fly ash concretes were noticeably increased as compared to those of the control concretes (without fly ash). This could possibly be due to the lower cement content of the high-volume fly ash concretes. Carette et al. 9 reported data on the setting time of high-volume (55 % to 60 %) Class F fly ash concretes. Eight sources of fly ashes and two sources of portland cements were used. The initial-and final-setting times varied from 4:50 to 12:51(hr: min), and 6:28 to 13:24 (hr: min), respectively, except for one mixture whose final-setting 4 time exceeded 13:24 (hr: min). Concrete mixtures showed varying setting times depending upon the source of fly ash. In general, for each fly ash source, concrete made with a low-alkali content cement having 6% C 3 A showed longer setting times than concrete made with a high-alkali content cement having 11.9% C 3 A. Malhotra and Ramezanianpour 10 have reported that inclusion of Class F fly ash retards the hydration of C 3 S at very early stages of hydration and then accelerate at later stages. C 3 A contribution from this fly ash increased with increasing its content as a replacement of cement. Thus, fly ash also became a contributor of C 3 A and other reactive components at high fly ash contents. Accelerated setting and hardening occurred due to the reactions of C 3 A present in the fly ash in addition to contributions of reactions associated with cement hydration in presence of fly ash at cement replacements of about 40% and above. Extremely high rate of setting and hardening occurred at 70% fly ash content and beyond due to the presence of relatively higher amount of C 3 A contributed by the fly ash, in addition to that contributed by cement. Hydration of aluminates was very rapid leading to formation of C 3 AH 6 , C 4 AH 19 , and C 2 AH 8 with generation of large amount of heat of hydration 13 . Eren et al. 11 reported the results of setting times of concrete incorporating up to 50 % ground-granulated blast-furnace slag (GGBS) under curing temperatures ranging from 6 to 80 o C. They concluded that: (1) increase in temperature decreased the setting times of concrete; (2) setting times of fly ash concretes were longer than those of Type I cement concretes and GGBS concretes; and (3) at temperatures greater than 20 o C, the setting times of GGBS concretes were shorter than those of Type I cement concretes. Pinto and Hover 12 studied the effects of inclusion of silica fume and superplasticizer on setting behavior of high-strength concrete mixtures. The influence of temperature was also studied by storing mortar specimens at different temperatures. Use of silica fume caused reduction in the initial time of setting. However, an opposite trend was noted when superplasticizer was used. Statistical analysis revealed significant interaction between the two (silica fume and superplasticizer) when the initial time of setting was taken as a response. The effect of temperature was significant on both initial and final times of setting. Samadi et al. 13 studied the influence of phosphogypsum (PG) on the times of setting and soundness of cement pastes. In this study, cement paste mixtures were made using ordinary portland cement (OPC) and pozzolanic portland cement (PPC) at a constant water to cement ratio of 0.6 with PG content varying between 0 and 100 percent. In general both initial and final times of setting increased with increasing PG content. The initial time of setting ranged between 100 to 560 minutes and 120 to 710 minutes for pastes containing OPC (ordinary portland cement) and PPC (pozzolana Portland cement), respectively. The corresponding final time of setting ranged between 250 to 1440 minutes and between 270 to 1440 minutes. The paste expansion also increased with increasing PG content. Brooks 14 investigated the effects of silica fume (SF), metakaolin (MK), fly ash (FA), and ground-granulated blast-furnace slag (GGBS) on the setting times of high-strength concrete using the penetration resistance method (ASTM C 403). He also studied the effects of shrinkage-reducing Admixture (SRA) on the setting times of normal and high-strength concretes. Based on the test results, he concluded that: (1) the setting times of the high-strength concrete were generally retarded when the mineral Admixtures replaced part of the cement. While the SRA was found to have negligible effect on the setting times of normal strength concrete, it exhibited a rather significant retarding effect when used in combination with a superplasticizer; and (2) the inclusion of GGBS at replacement levels of 40% and greater resulted in significant retardation in setting times. In general, as replacement levels of the mineral Admixtures were increased, there was greater 5 retardation in setting times. However, for the concrete containing MK, setting time were only observed up to a replacement level of 10%. Ahmadi 15 studied the initial and final setting times of concrete in hot weather. The effect of field temperature, relative humidity, wind velocity, and Admixture on the setting times of concrete were observed. He proposed two equations: (1) the first equation was for determining the initial setting time of concrete with a correlation factor of 0.93 and standard deviation of 5.28%. This equation showed that as the field temperature and field air velocity increased, the initial setting time decreased, and as the field humidity increased, the initial setting time increased; and (2) the second equation for determining the final setting time of concrete with a correlation factor of 0.9 and standard deviation of 5.8% showed similar effects as of initial setting time of concrete. Targan et al. Takemoto and Uchikawa 18 and Uchiwaka and Uchida 19 described a model for hydration reaction process of cement in the presence of pozzolans. The reactions of C 3 A and Class C fly ash resulted in formation of enttringite, monosulphoaluminate hydrate, calcium aluminate hydrates, and calcium silicate hydrate. They reported that presence of pozzolan accelerated hydration of C 3 A due to adsorbing Ca 2+ from the liquid phases and providing precipitation sites for the hydration products. Tay 20 performed a study to investigate properties of mortar and concrete as influenced by inclusion of pulverized sludge ash. The test data exhibited improved workability and increase in initial and final times of setting with increasing sludge ash content. Sawan and Qasrawi 21 concluded that the use of natural pozzolan cause decrease in workability and increase in the times of setting of mortar under normal condition. However, an opposite trend was obtained in hot weather conditions. Uchikawa et al. 22 evaluated the effects of chemical Admixtures on the hydration characteristics of cement. They reported that an Admixture having a functional group that produces complex salt with decrease in Ca 2+ concentration can cause loss in fluidity and delay in the times of setting of cement pastes. Chen and Older 23 investigated the effect of cement with varying in clinker composition with varying amounts and forms of calcium sulfate on the times of setting of mortars. 6 They indicated that the setting of cement having normal composition was mainly related to hydration of C 3 S content. The formation of enttringite occurred at very high C 3 A contents. Matusinovic and Vrbos 24 and Matusinovic and Curlin 25 reported that setting characteristics of high-alumina cement (HAC) were substantially influenced by inclusion of alkali metal salts. The lithium cation had a greater effect on the times of setting than alkali cations did. The results showed that lithium salt or alkali metal salts could be used as a set accelerator for HAC. Perret et al. 26 investigated the compatibility of six different microfine cements and four different HRWRAs; and the influence of materials and mixture proportions on rheological characteristics and final-setting time of microfine cement-based grouts. Three portland cements and three slag cements, associated with various naphthalene-based and melamine-based HRWRA were investigated. They concluded that: (1) not every microfinecement can be used with every HRWRA; (2) some HRWRAs gave better fluidity, and some gave too long (24 hours) or too short (4 hours) final setting times; and (3) the chemical composition and fineness of cements, as well as the type and chemical characteristics of Admixtures lead to different grout properties. INFLUENCE OF FLY ASH ON SETTING TIMES OF NON-AIR-AIR ENTRAINED CONCRETES (Series 1) Experimental Details An experimental program was designed to evaluate the effects of Class C fly ash content and its source on setting times of non air-entrained concrete. Four different Class C fly ashes, obtained from different electric power plants in Wisconsin, were used. The fly ashes corresponding to these power plants are designated as P-4, DPC, Columbia, and Weston. Chemical and physical properties of these fly ashes were determined. Three of the fly ashes (DPC, Columbia, and Weston) exceeded ASTM C 618 requirement for MgO. However, they met all other ASTM C 618 Class C fly ash requirement. Natural sand with 6 mm maximum size was used as a fine aggregate, and a 19 mm maximum size gravel was used as a coarse aggregate throughout this investigation. These aggregates met the ASTM C 33 requirements. Type I cement which met the requirements of ASTM C 150 was used. Concrete mixture proportions were proportioned with all the four Class C fly ashes. Results and Discussion Initial and final setting times of concrete incorporating various sources of Class C fly ash are shown in At high replacements of cement with fly ash (70% or above), the setting of concrete was accelerated. This might be attributed to the fact that at higher cement replacements with fly ash, the concentrations of total C 3 A and gypsum present in the mixture becomes low. This resulted in reduced setting times of the mixtures containing low cement and high fly ash contents. As a result, rapid setting of the concrete mixtures occurred. Therefore, under such conditions, it is desirable to use a set retarding Admixtures to allow enough time for proper mixing and placing of concrete. SETTING TIMES OF NON-AIR-ENTRAINED AND AIR-ENTRAINED FLY ASH CONCRETE (Series 2) Experimental Details One source (Pleasant Prairie Power Plant, P-4) of Class C fly ash was used. Three nominal compressive strength levels (21, 28, and 35 MPa) of non-air-entrained and air-entrained concrete mixture proportions, by varying the water-to-cementitious materials ratio (0.45, 0.55, and 0.65) were developed. Cement replacement percentage was 35, 45, and 55%. Replacement was on the basis of Results and Discussion Setting time of non-air-entrained concrete mixtures are given in Setting time data for air-entrained concrete are given in 9 SETTING TIMES OF CEMENT PASTE AS INFLUENCED BY FLY ASH AND CHEMICAL AdmixtureS Four series of tests were performed: (1) to evaluate only the effects of fly ash addition on the setting times of cement paste; (2) to evaluate the effects of fly ash and two levels of air content on the setting times of cement paste; and (3) to evaluate the influence of fly ash and normal dosage of two types of chemical Admixtures (WRA and HRWRA) on the setting times of cement paste; (4) to evaluate the combined effects high dosage of fly ash and three dosage rates of two types of chemical Admixtures (retarders and gypsum) on the setting times of cement paste. Experimental Details A portland cement conforming to the requirements of ASTM C 150 was used. An ASTM Class C fly ash, obtained from one source, Pleasant Prairie (P-4), was used. The fly ash met all ASTM C 618 requirements for Class C fly ash. Five chemical Admixtures: an air entraining Admixture (ASTM C 260), a water-reducer (ASTM C 494, Type A), a retarder (ASTM C 494, Type B), and a HRWRA (ASTM C 494, Type F) were obtained from a local ready-mixed concrete company, the Tews Company, Milwaukee, WI. A total of 82 cement paste mixtures were prepared for evaluating their setting and hardening characteristics. Each mixture was composed of cement, fly ash, and water. Fly ash was used as a replacement of cement ranging from 0 to 100 percent by mass. A ratio of fly ash addition to cement replaced was kept at 1.25. All ingredients were mixed in a laboratory mixer in accordance with ASTM C 305. Normal consistency of pastes containing cement/fly ash was determined in accordance with ASTM C 187. Air content of each paste mixture was determined according to ASTM C 185. Test specimens for each mixture were prepared for measuring the initial and final times of setting using the Vicat apparatus (ASTM C 191). Results and Discussion Effect of fly ash on setting times of pastes without Admixtures The initial and final times of setting were essentially the same due to the inclusion of fly ash at 10% compared to the 0% fly ash mixture Effect of air entrainment and content on setting times of paste Effects of air entrainment and content at two dosage levels on setting times of fly ash mixtures are given in Effect of fly ash with normal dosages of chemical Admixtures on setting times of paste In this series of tests, fly ash content varied from 0 to 100% with normal dosages of individual chemical Admixtures (five different types). Fly ash with a normal dosage of water-reducer Effects of normal dosage of water-reducer on setting characteristics of fly ash mixtures are given in Fly ash with a normal dosage of superplasticizer Effects of normal dosage of superplasticizer on setting characteristics of fly ash mixtures are given in Fly ash with a normal dosage of retarder Effects of normal dosage of retatder on setting characteristics of fly ash mixtures are given in Fly ash with a normal dosage of gypsum Effects of normal dosage of gypsum on setting characteristics of fly ash mixtures are given in Effect of High Fly Ash Contents with High Dosages of Chemical Admixtures on Setting Times of Paste At high fly ash content (above 40%), very rapid rate of setting of mixtures occurred. Use of normal dosage of retarder and gypsum did not cause enough delay to compensate for the rapid rate of setting resulting from the presence of the high-levels of fly ash. Therefore, high dosages of these Admixtures were used at fly ash contents of 70, 85, and 100%. The retarder and gypsum were used at their respective double and triple dosages. Fly ash with retarder Effects of high dosage of retatder on setting characteristics of fly ash mixtures are given in Fly ash with gypsum Effects of high dosage of gypsum on setting characteristics of fly ash mixtures are given in CONCLUSIONS Following are the general conclusions from this study: 1. Both the initial-and final-setting times of the concretes were significantly influenced by both the source and amount of fly ash. Both the initial-and final-setting times were relatively unaffected at 10% cement replacement. Although inclusion of fly ash caused large retardation in the setting times, for up to around 60% cement replacement, the rate of strength development were appropriate for most construction applications. Therefore, setting time should not be taken as a sole parameter for selecting a fly ash for a particular 12 application. However, in order to improve construction productivity and efficient construction planning, fly ash content should be reduced and/or chemical Admixtures should be added to control the setting times. 2. For non-air-entrained and air-entrained fly ash concretes having compressive strengths of 21, 28, and 35 MPa, the in
-
characterization of lightweight mortars containing wood processing by products waste
Construction and Building Materials, 2016Co-Authors: Valeria Corinaldesi, Alida Mazzoli, Rafat SiddiqueAbstract:Abstract In this study wood processing by-products were used by replacing natural sand for producing lightweight mortars. Manufacturers of wood products and furniture generate sawdust and pieces of side-cuts from a log to rectangular shapes. These are also produced by cutting, drilling, and milling operations when a wood piece is cut either from wood logs or while preparing finished products. Saw dust is often collected in filter bags or dust collectors. Three different percentages of substitution of natural sand were tried: 2.5%, 5%, and 10% by volume of the sand. Wood by-products were always pre-soaked in water and sometimes in calcium hydroxide aqueous solution in order to obtain wood mineralization before addition to the mortar mixture. Mortars containing wood by-products were characterized by means of compression and bending tests, drying shrinkage, resistance to water vapour permeability, water capillary absorption, and thermal conductivity measurements. Results obtained showed that a maximum dosage of 5% wood by-products should be used in order to avoid an excessive loss of mortar mechanical strength, and due to the reduction of thermal conductivity of about 25%. On the other hand, if a water reducing Admixture is added, adequate mechanical performance can be obtained even with 10% wood by-products.
Ramyar Kambiz - One of the best experts on this subject based on the ideXlab platform.
-
Effect of false set related anomalies on rheological properties of cement paste mixtures in the presence of high range water reducing Admixture
'Wiley', 2020Co-Authors: Mardani-aghabaglou Ali, Felekoglu Burak, Ramyar KambizAbstract:felekoglu, burak/0000-0002-7426-1698WOS: 000561439400001There are many studies related to the fresh state properties of the cementitious systems in the literature. However, there is no specific study about the effects of false set formation on fresh state properties of these systems. in this study, the effect of false set formation on fresh state and rheological properties of the cement paste mixtures containing high range water reducing (HRWR) Admixture was investigated experimentally. For this aim, two different commercial CEMI 42.5 R. type cements produced by different companies were used. in order to investigate the effect of false set formation related anomalies on fresh state properties, paste mixtures were prepared with different mixing times. in the mixtures where false set related anomaly was the case, rheological properties were positively affected by prolonging the mixing time.Turkish Cement Manufacturers AssociationTurkish Cement Manufacturers Associatio
-
Improving the mechanical and durability performance of recycled concrete aggregate-bearing mortar mixtures by using binary and ternary cementitious systems
'Elsevier BV', 2019Co-Authors: Mardani-aghabaglou Ali, Yuksel Cihat, Beglarigale Ahsanollah, Ramyar KambizAbstract:WOS: 000456755400027Environmental concerns arising from the generation of huge amount of construction and demolition waste requires recycling this material, which would otherwise be sent to landfill. The mechanical and durability performance of mortar mixtures containing recycled concrete (RC) aggregate was investigated in this study. Although it is known that the adhered mortar creates a porous and a weak additional interfacial transition zone in recycled aggregate-bearing mixture, the dependence of the behavior on the type of new matrix should be searched in detail. For this purpose, compressive strength, ultrasound pulse velocity, water absorption, chloride ion penetration, freeze-thaw and sulfate resistance as well as drying shrinkage tests were conducted on mortar mixtures containing either natural aggregate (sand) or recycled concrete aggregate. Scanning electron micrographs and optical microscope images were obtained on specimens exposed to sulfate attack. The mineral Admixtures used in the study included silica fume (SF), metakaolin (MK) and a Class C fly ash (FA). In addition to the control mixture including no mineral Admixture (PC), silica fume- and metakaolin-incorporating binary systems (PC-SF and PC-MK) were prepared. Besides, two ternary systems, i.e., PC-SF-FA and PC-MK-FA were also designed. The results indicated a gradual strength gain beyond 28 days and reduction in initial shrinkage values in RC-bearing mixtures, compared to those of the sand-bearing mixtures. Besides, the porous character of RC helped reducing the internal pressure and resultant damage related with expanding water and swelling ettringite crystals in freeze-thaw and sulfate attack tests, respectively. The exact effect of recycled aggregate on mortar properties was found to be greatly dependent on the type of the cementitious system of the new mix. (C) 2018 Elsevier Ltd. All rights reserved.Uludag University Scientific Research Projects Centre (BAP) [KUAP(MH)-2017/11]The authors would like to thank Izmir Cimentas Cement Plant and Polisan Construction Chemicals Company authorities for their kind assistance in providing the cement, mineral Admixture and water reducing Admixture as well as determining the chemical composition, physical and mechanical properties of these products. Besides, the first author gratefully acknowledge support provided by Uludag University Scientific Research Projects Centre (BAP) under Grant numbers KUAP(MH)-2017/11
-
EFFECT OF CEMENT FINENESS ON PROPERTIES OF CEMENTITIOUS MATERIALS CONTAINING HIGH RANGE WATER REDUCING Admixture
'College Publishing', 2017Co-Authors: Mardani-aghabaglou Ali, Felekoglu Burak, Son, Arif Emre, Ramyar KambizAbstract:WOS: 000396529300009The effect of cement fineness on the fresh state and rheological properties as well as compressive strength of cementitious systems was investigated. A CEM I 42.5R portland cement containing 7.92% C(3)A and sulfate resisting cement containing 3.58% C(3)A were used. The cements were ground to 4 different Blaine finenesses, ranging from 2800 to 4500 cm(2)/g. In the absence of Water-Reducing Admixture, the water requirement of mixtures increased with an increase in the cement fineness. Thus, the fresh state properties of the mixtures were affected negatively. However, surprisingly, a reverse behavior was observed in the mixtures containing Water-Reducing Admixtures, that is, an increase of the cement fineness increased the effectiveness of the Admixture; consequently, the fresh state properties of the mixtures were improved. This seems to have been caused from the higher adsorption of the Admixture on finer cement grains than on the coarser particles. Moreover, as expected, the strength of the mortar and concrete mixtures increased along with the increase in cement fineness and its C3A content.Turkish Cement Manufacturers AssociationThe authors would like to thank Izmir-Cimentas and Akcansa cement plants for their kind assistance in providing the cements and determining the chemical composition of the cements. The first author would like to acknowledge the scholarship provided by Turkish Cement Manufacturers Association during his PhD study
-
Effect of gypsum type on properties of cementitious materials containing high range water reducing Admixture
'Elsevier BV', 2016Co-Authors: Mardani-aghabaglou Ali, Boyaci, Onur Can, Hosseinnezhad Hojjat, Felekoglu Burak, Ramyar KambizAbstract:WOS: 000373650700003In this study, the effect of cement gypsum type on properties of the properties of cement paste, mortar and concrete mixtures containing high range water reducing Admixture (HRWR) was investigated. Two different types of cement prepared from the same clinker but containing either calcium sulfate hemihydrate or dihydrate as retarder were used. The fresh and hardened (compressive strength and drying shrinkage) properties as well as static and dynamic rheological behavior of the mixtures were investigated. Compared to the mixtures containing dihydtate, the fresh and rheological properties of mixtures were negatively affected when cement-containing hemihydrate was used. However, hemihydrate utilization had a positive influence on the early compressive strength. The adverse effects on fresh properties were more significant in paste mixtures. These negative effects decreased in the mortar and concrete mixtures. The presence of hemihydrate in cement was found to increase the drying-shrinkage. (C) 2016 Elsevier Ltd. All rights reserved.Turkish Cement Manufacturers AssociationThe authors would like to thank Izmir-Cimentas cement plant for their kind assistance in providing the cement and determining the chemical composition of the cement. The first author would like to acknowledge the scholarship provided by Turkish Cement Manufacturers Association during his PhD study
Bruce W Ramme - One of the best experts on this subject based on the ideXlab platform.
-
Center for By-Products Utilization USE OF FOUNDRY INDUSTRY SILICA-DUST IN MANUFACTURING ECONOMICAL SELF- CONSOLIDATING CONCRETE Use of Foundry Industry Silica-Dust in Manufacturing Economical Self-Consolidating Concrete
2020Co-Authors: Tarun R Naik, Yoonmoon Chun, Rudolph N Kraus, Rakesh Kumar, Bruce W Ramme, T R Naik, Y ChunAbstract:Synopsis: Results of an experimental work conducted on the use of foundry industry silica-dust in manufacturing economical self-consolidating concrete (SCC) are presented in this paper. Class C fly ash was used as a replacement for up to 35% of cement by mass. Silica-dust obtained from an iron foundry, collected by a high-efficiency baghouse, was used as a replacement for 10, 20, and 30% of the fly ash at 2:1 (foundry dust -fly ash) ratio by mass. The extra amount of foundry dust was treated as a partial replacement for sand. Use of foundry dust in SCC resulted in high air content (7 -10%) and low density of concrete due to reaction between foundry dust and the particular brands of chemical Admixtures used. Further, with the increase in foundry dust content containing iron, the color of concrete changed from dark gray to black. For the foundry silica-dust content of 20% and above, the requirement for high-range Water-Reducing Admixture [HRWRA] increased; however, the amount of viscosity-modifying Admixture [VMA]) decreased up to 33% up to the silica-dust content of 30%. It was concluded that foundry industry silica-dust material can be used for partial replacement of cement, fly ash, and sand in SCC. More extensive work is in progress. [1995][1996][1997][1998][1999][2000]. Rudolph N. Kraus is Assistant Director of the UWM-CBU. He has been involved with numerous projects on the use of by-product materials including utilization of foundry sand and fly ash in CLSM and SCC, evaluation of lightweight aggregates, and use of by-product materials in the production of ready-mixed concrete and cast-concrete products. Yoon-moon Chun is a Research Associate at the UWM-CBU. His research interests include the use of coal fly ash, coal bottom ash, and used foundry sand in concrete and dry and wet cast-concrete products, and the use of fibrous residuals from pulp and paper mills in concrete. Rakesh Kumar is a Scientist in Bridges Division of Central Road Research Institute, New Delhi, India. He was formerly at the UWM-CBU as a Research Associate. His research interest includes pore structure of concrete, high-performance concrete, self-consolidating concrete, repair and rehabilitation of distressed structures, and durability of concrete. INTRODUCTION Self-consolidating concrete (SCC), a recent innovation in concrete technology, has numerous advantages over conventional concrete. Self-consolidating concrete, as the name indicates, is a type of concrete that does not require external or internal compaction, because it becomes leveled and consolidated under its self-weight. SCC can spread and fill all corners of the formwork, purely by means of its self-weight, thus eliminating the need of vibration or any type of consolidating effort Hoshimoto et al. Meht
-
Center for By-Products Utilization INFLUENCE OF FLY ASH AND CHEMICAL AdmixtureS ON THE SETTING TIME OF CEMENT PASTE AND CONCRETE Influence of Fly Ash and Chemical Admixtures on the Setting Time of Cement Paste and Concrete INFLUENCE OF FLY ASH ON SETTING
2020Co-Authors: Rafat Siddique, Tarun R Naik, Bruce W RammeAbstract:Synopsis: A recurring question about use of fly ash in concrete is dealing with setting and hardening of such mixtures with our with out chemical Admixtures. This paper presents literature review on the setting and hardening characteristics of cement paste and concrete as influenced by the inclusion of fly ash and chemical Admixtures. The paper also reports the work carried out at the University of Wisconsin-Milwaukee (UWM-CBU) on the effects of Class C fly ashes from various sources on the initial-and final-setting times of non-air-entrained and air-entrained concrete; and the effects of Class C fly ash, gypsum, and various types of chemical Admixtures (air-entraining Admixture (AEA), Water-Reducing Admixture (WRA), superplasticizer, and retarding Admixture) on the initial and final setting times of cement paste. Test results indicated that: (1) both the initial-and final-setting times were relatively unaffected at low-percentage replacement of cement with Class C fly ash, although inclusion of fly ash caused large retardation in the times of setting, up to around 60 percent cement replacement; (2) initial-and final-setting times of cement paste remained essentially the same or were slightly delayed with up to 20 percent cement replacement relative to zero percent fly ash content; beyond this range, the setting times of cement paste were accelerated. Increased rate of setting occurred at cement replacement levels of 40 percent and higher irrespective of type of chemical Admixtures used. Keywords: Air-entraining Admixture (AEA), concrete, fly ash, gypsum, high-range Water-Reducing Admixture (HRWRA), paste, retarder, time of setting, Water-Reducing Admixture. INTRODUCTION Immediately upon mixing of cement and water, various chemical reactions occur leading to formation of numerous types of hydration products. The types and amount of hydration products formed depend upon duration of hydration, water-cementitious materials ratio (W/Cm), properties of constituent materials, temperature, soluble alkalis, and mineral and chemical Admixtures. The formation of hydration products causes increase in stiffness of the cementitious matrix. This stiffening behavior of the matrix is determined by the times of initial and final setting. The initial setting of the matrix refers to the beginning of solidification for a given mixture. It is generally accepted that at this stage concrete can neither be properly re-tamped nor handled or placed. The final setting refers to the stage when the mixture attains sufficient hardness to support stress. The subsequent continuing strength gain is called hardening. Setting and hardening of cement mortar mixtures are considerably influenced by inclusion of either mineral or chemical Admixtures. Generally, the setting and hardening of mortar are delayed when ASTM Class F (low-lime) fly ash is added to it. Mortar incorporating ASTM Class C (highlime) fly ash, however, has shown either both rapid or delayed setting depending upon the properties and amount of the ash. The setting behavior can be more readily modified when gypsum and chemical Admixtures such as Water-Reducing Admixture (WRA), superplasticizer, or retarding and accelerating Admixture are used. Even air-entraining Admixture is known to slightly modify setting behavior of concrete. A knowledge of setting characteristics of concrete incorporating both mineral and chemical Admixtures is needed for efficient scheduling of concrete construction, specifically floor slabs, roadways, pavements, and other flat surfaces. Limited data exist on setting and hardening behavior of paste, mortar, and concrete containing ASTM Class C fly ash and chemical Admixtures. 3 LITERATURE REVIEW Many investigators have reported on the effects of fly ash on the times of setting of cement paste and concrete. Dodson 1 investigated the setting characteristics of concretes made with both Class C and Class F fly ashes. He reported that the setting times of concrete are mainly governed by cement content and W/Cm when all other parameters are kept equal. He further added that an increase in cement content caused a decrease in the initial-and final-setting times, whereas an increase in W/Cm increased setting times. However, in general, addition of fly ash increased the setting times. Ramakrishnan et al. 2 reported on the setting characteristics of concretes made with or without fly ash. They used one high-lime fly ash and two types of cement (ASTM Type I and Type II). They concluded that inclusion of fly ash resulted in higher initial-and final-setting times compared to the concrete without fly ash for both types of cement. Lane and Best 3 reported that fly ash generally slows the setting of concrete, although both initial and final times of setting remain within specified limits. Retardation of setting due to the inclusion fly ash may be affected by the amount, fineness, and chemical composition (particularly, carbon content) of the ash. However, the fineness of cement, the water content of the cementitious paste, and the ambient temperature usually have a much greater effect on times of setting than addition of fly ash. Replacement of 60% of cement with high-carbon fly ash by mass resulted in 200% increase in the time of final setting of control concrete mixture. . Gebler and Klieger 6 studied the times of setting of concretes containing Class F and Class C fly ashes from 10 different sources for high content mixtures. They reported that inclusion of the fly ash increased the initial-and finalsetting times of concrete mixtures. Carette and Malhotra 7 reported the setting characteristics of concretes made with fly ashes from different sources. Calcium oxide (CaO) contents of the fly ashes varied between 1 % and 13 %. They concluded that, in general, the fly ashes increased the initial-and final-setting times of concrete. Bilodeau and Malhotra 8 reported properties of concrete incorporating high volumes of Class F fly ashes from three different sources. Cementitious materials content was 300, 370 and 430 kg/m 3 , and three W/Cm (0.39, 0.31 and 0.27) were used. They concluded that for every W/Cm, the initial-and final-setting times of high-volume fly ash concretes were noticeably increased as compared to those of the control concretes (without fly ash). This could possibly be due to the lower cement content of the high-volume fly ash concretes. Carette et al. 9 reported data on the setting time of high-volume (55 % to 60 %) Class F fly ash concretes. Eight sources of fly ashes and two sources of portland cements were used. The initial-and final-setting times varied from 4:50 to 12:51(hr: min), and 6:28 to 13:24 (hr: min), respectively, except for one mixture whose final-setting 4 time exceeded 13:24 (hr: min). Concrete mixtures showed varying setting times depending upon the source of fly ash. In general, for each fly ash source, concrete made with a low-alkali content cement having 6% C 3 A showed longer setting times than concrete made with a high-alkali content cement having 11.9% C 3 A. Malhotra and Ramezanianpour 10 have reported that inclusion of Class F fly ash retards the hydration of C 3 S at very early stages of hydration and then accelerate at later stages. C 3 A contribution from this fly ash increased with increasing its content as a replacement of cement. Thus, fly ash also became a contributor of C 3 A and other reactive components at high fly ash contents. Accelerated setting and hardening occurred due to the reactions of C 3 A present in the fly ash in addition to contributions of reactions associated with cement hydration in presence of fly ash at cement replacements of about 40% and above. Extremely high rate of setting and hardening occurred at 70% fly ash content and beyond due to the presence of relatively higher amount of C 3 A contributed by the fly ash, in addition to that contributed by cement. Hydration of aluminates was very rapid leading to formation of C 3 AH 6 , C 4 AH 19 , and C 2 AH 8 with generation of large amount of heat of hydration 13 . Eren et al. 11 reported the results of setting times of concrete incorporating up to 50 % ground-granulated blast-furnace slag (GGBS) under curing temperatures ranging from 6 to 80 o C. They concluded that: (1) increase in temperature decreased the setting times of concrete; (2) setting times of fly ash concretes were longer than those of Type I cement concretes and GGBS concretes; and (3) at temperatures greater than 20 o C, the setting times of GGBS concretes were shorter than those of Type I cement concretes. Pinto and Hover 12 studied the effects of inclusion of silica fume and superplasticizer on setting behavior of high-strength concrete mixtures. The influence of temperature was also studied by storing mortar specimens at different temperatures. Use of silica fume caused reduction in the initial time of setting. However, an opposite trend was noted when superplasticizer was used. Statistical analysis revealed significant interaction between the two (silica fume and superplasticizer) when the initial time of setting was taken as a response. The effect of temperature was significant on both initial and final times of setting. Samadi et al. 13 studied the influence of phosphogypsum (PG) on the times of setting and soundness of cement pastes. In this study, cement paste mixtures were made using ordinary portland cement (OPC) and pozzolanic portland cement (PPC) at a constant water to cement ratio of 0.6 with PG content varying between 0 and 100 percent. In general both initial and final times of setting increased with increasing PG content. The initial time of setting ranged between 100 to 560 minutes and 120 to 710 minutes for pastes containing OPC (ordinary portland cement) and PPC (pozzolana Portland cement), respectively. The corresponding final time of setting ranged between 250 to 1440 minutes and between 270 to 1440 minutes. The paste expansion also increased with increasing PG content. Brooks 14 investigated the effects of silica fume (SF), metakaolin (MK), fly ash (FA), and ground-granulated blast-furnace slag (GGBS) on the setting times of high-strength concrete using the penetration resistance method (ASTM C 403). He also studied the effects of shrinkage-reducing Admixture (SRA) on the setting times of normal and high-strength concretes. Based on the test results, he concluded that: (1) the setting times of the high-strength concrete were generally retarded when the mineral Admixtures replaced part of the cement. While the SRA was found to have negligible effect on the setting times of normal strength concrete, it exhibited a rather significant retarding effect when used in combination with a superplasticizer; and (2) the inclusion of GGBS at replacement levels of 40% and greater resulted in significant retardation in setting times. In general, as replacement levels of the mineral Admixtures were increased, there was greater 5 retardation in setting times. However, for the concrete containing MK, setting time were only observed up to a replacement level of 10%. Ahmadi 15 studied the initial and final setting times of concrete in hot weather. The effect of field temperature, relative humidity, wind velocity, and Admixture on the setting times of concrete were observed. He proposed two equations: (1) the first equation was for determining the initial setting time of concrete with a correlation factor of 0.93 and standard deviation of 5.28%. This equation showed that as the field temperature and field air velocity increased, the initial setting time decreased, and as the field humidity increased, the initial setting time increased; and (2) the second equation for determining the final setting time of concrete with a correlation factor of 0.9 and standard deviation of 5.8% showed similar effects as of initial setting time of concrete. Targan et al. Takemoto and Uchikawa 18 and Uchiwaka and Uchida 19 described a model for hydration reaction process of cement in the presence of pozzolans. The reactions of C 3 A and Class C fly ash resulted in formation of enttringite, monosulphoaluminate hydrate, calcium aluminate hydrates, and calcium silicate hydrate. They reported that presence of pozzolan accelerated hydration of C 3 A due to adsorbing Ca 2+ from the liquid phases and providing precipitation sites for the hydration products. Tay 20 performed a study to investigate properties of mortar and concrete as influenced by inclusion of pulverized sludge ash. The test data exhibited improved workability and increase in initial and final times of setting with increasing sludge ash content. Sawan and Qasrawi 21 concluded that the use of natural pozzolan cause decrease in workability and increase in the times of setting of mortar under normal condition. However, an opposite trend was obtained in hot weather conditions. Uchikawa et al. 22 evaluated the effects of chemical Admixtures on the hydration characteristics of cement. They reported that an Admixture having a functional group that produces complex salt with decrease in Ca 2+ concentration can cause loss in fluidity and delay in the times of setting of cement pastes. Chen and Older 23 investigated the effect of cement with varying in clinker composition with varying amounts and forms of calcium sulfate on the times of setting of mortars. 6 They indicated that the setting of cement having normal composition was mainly related to hydration of C 3 S content. The formation of enttringite occurred at very high C 3 A contents. Matusinovic and Vrbos 24 and Matusinovic and Curlin 25 reported that setting characteristics of high-alumina cement (HAC) were substantially influenced by inclusion of alkali metal salts. The lithium cation had a greater effect on the times of setting than alkali cations did. The results showed that lithium salt or alkali metal salts could be used as a set accelerator for HAC. Perret et al. 26 investigated the compatibility of six different microfine cements and four different HRWRAs; and the influence of materials and mixture proportions on rheological characteristics and final-setting time of microfine cement-based grouts. Three portland cements and three slag cements, associated with various naphthalene-based and melamine-based HRWRA were investigated. They concluded that: (1) not every microfinecement can be used with every HRWRA; (2) some HRWRAs gave better fluidity, and some gave too long (24 hours) or too short (4 hours) final setting times; and (3) the chemical composition and fineness of cements, as well as the type and chemical characteristics of Admixtures lead to different grout properties. INFLUENCE OF FLY ASH ON SETTING TIMES OF NON-AIR-AIR ENTRAINED CONCRETES (Series 1) Experimental Details An experimental program was designed to evaluate the effects of Class C fly ash content and its source on setting times of non air-entrained concrete. Four different Class C fly ashes, obtained from different electric power plants in Wisconsin, were used. The fly ashes corresponding to these power plants are designated as P-4, DPC, Columbia, and Weston. Chemical and physical properties of these fly ashes were determined. Three of the fly ashes (DPC, Columbia, and Weston) exceeded ASTM C 618 requirement for MgO. However, they met all other ASTM C 618 Class C fly ash requirement. Natural sand with 6 mm maximum size was used as a fine aggregate, and a 19 mm maximum size gravel was used as a coarse aggregate throughout this investigation. These aggregates met the ASTM C 33 requirements. Type I cement which met the requirements of ASTM C 150 was used. Concrete mixture proportions were proportioned with all the four Class C fly ashes. Results and Discussion Initial and final setting times of concrete incorporating various sources of Class C fly ash are shown in At high replacements of cement with fly ash (70% or above), the setting of concrete was accelerated. This might be attributed to the fact that at higher cement replacements with fly ash, the concentrations of total C 3 A and gypsum present in the mixture becomes low. This resulted in reduced setting times of the mixtures containing low cement and high fly ash contents. As a result, rapid setting of the concrete mixtures occurred. Therefore, under such conditions, it is desirable to use a set retarding Admixtures to allow enough time for proper mixing and placing of concrete. SETTING TIMES OF NON-AIR-ENTRAINED AND AIR-ENTRAINED FLY ASH CONCRETE (Series 2) Experimental Details One source (Pleasant Prairie Power Plant, P-4) of Class C fly ash was used. Three nominal compressive strength levels (21, 28, and 35 MPa) of non-air-entrained and air-entrained concrete mixture proportions, by varying the water-to-cementitious materials ratio (0.45, 0.55, and 0.65) were developed. Cement replacement percentage was 35, 45, and 55%. Replacement was on the basis of Results and Discussion Setting time of non-air-entrained concrete mixtures are given in Setting time data for air-entrained concrete are given in 9 SETTING TIMES OF CEMENT PASTE AS INFLUENCED BY FLY ASH AND CHEMICAL AdmixtureS Four series of tests were performed: (1) to evaluate only the effects of fly ash addition on the setting times of cement paste; (2) to evaluate the effects of fly ash and two levels of air content on the setting times of cement paste; and (3) to evaluate the influence of fly ash and normal dosage of two types of chemical Admixtures (WRA and HRWRA) on the setting times of cement paste; (4) to evaluate the combined effects high dosage of fly ash and three dosage rates of two types of chemical Admixtures (retarders and gypsum) on the setting times of cement paste. Experimental Details A portland cement conforming to the requirements of ASTM C 150 was used. An ASTM Class C fly ash, obtained from one source, Pleasant Prairie (P-4), was used. The fly ash met all ASTM C 618 requirements for Class C fly ash. Five chemical Admixtures: an air entraining Admixture (ASTM C 260), a water-reducer (ASTM C 494, Type A), a retarder (ASTM C 494, Type B), and a HRWRA (ASTM C 494, Type F) were obtained from a local ready-mixed concrete company, the Tews Company, Milwaukee, WI. A total of 82 cement paste mixtures were prepared for evaluating their setting and hardening characteristics. Each mixture was composed of cement, fly ash, and water. Fly ash was used as a replacement of cement ranging from 0 to 100 percent by mass. A ratio of fly ash addition to cement replaced was kept at 1.25. All ingredients were mixed in a laboratory mixer in accordance with ASTM C 305. Normal consistency of pastes containing cement/fly ash was determined in accordance with ASTM C 187. Air content of each paste mixture was determined according to ASTM C 185. Test specimens for each mixture were prepared for measuring the initial and final times of setting using the Vicat apparatus (ASTM C 191). Results and Discussion Effect of fly ash on setting times of pastes without Admixtures The initial and final times of setting were essentially the same due to the inclusion of fly ash at 10% compared to the 0% fly ash mixture Effect of air entrainment and content on setting times of paste Effects of air entrainment and content at two dosage levels on setting times of fly ash mixtures are given in Effect of fly ash with normal dosages of chemical Admixtures on setting times of paste In this series of tests, fly ash content varied from 0 to 100% with normal dosages of individual chemical Admixtures (five different types). Fly ash with a normal dosage of water-reducer Effects of normal dosage of water-reducer on setting characteristics of fly ash mixtures are given in Fly ash with a normal dosage of superplasticizer Effects of normal dosage of superplasticizer on setting characteristics of fly ash mixtures are given in Fly ash with a normal dosage of retarder Effects of normal dosage of retatder on setting characteristics of fly ash mixtures are given in Fly ash with a normal dosage of gypsum Effects of normal dosage of gypsum on setting characteristics of fly ash mixtures are given in Effect of High Fly Ash Contents with High Dosages of Chemical Admixtures on Setting Times of Paste At high fly ash content (above 40%), very rapid rate of setting of mixtures occurred. Use of normal dosage of retarder and gypsum did not cause enough delay to compensate for the rapid rate of setting resulting from the presence of the high-levels of fly ash. Therefore, high dosages of these Admixtures were used at fly ash contents of 70, 85, and 100%. The retarder and gypsum were used at their respective double and triple dosages. Fly ash with retarder Effects of high dosage of retatder on setting characteristics of fly ash mixtures are given in Fly ash with gypsum Effects of high dosage of gypsum on setting characteristics of fly ash mixtures are given in CONCLUSIONS Following are the general conclusions from this study: 1. Both the initial-and final-setting times of the concretes were significantly influenced by both the source and amount of fly ash. Both the initial-and final-setting times were relatively unaffected at 10% cement replacement. Although inclusion of fly ash caused large retardation in the setting times, for up to around 60% cement replacement, the rate of strength development were appropriate for most construction applications. Therefore, setting time should not be taken as a sole parameter for selecting a fly ash for a particular 12 application. However, in order to improve construction productivity and efficient construction planning, fly ash content should be reduced and/or chemical Admixtures should be added to control the setting times. 2. For non-air-entrained and air-entrained fly ash concretes having compressive strengths of 21, 28, and 35 MPa, the in
