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Weerachart Tangchirapat - One of the best experts on this subject based on the ideXlab platform.

  • influence of fly ash on Slump Loss and strength of concrete fully incorporating recycled concrete aggregates
    Journal of Materials in Civil Engineering, 2013
    Co-Authors: Weerachart Tangchirapat, Rak Buranasing, Chaiyanunt Rattanashotinunt, Chai Jaturapitakkul
    Abstract:

    This paper investigates the effects of fineness and replacement of fly ash on the fresh and hardened properties of recycled aggregate concrete. Two groups of recycled aggregate concretes were studied and compared with that of conventional concrete (CON) in which crushed limestone and local river sand were used as aggregates. The first group was prepared using 100% coarse recycled concrete aggregate and local river sand. For the second group, crushed limestone and local river sand were fully replaced by both coarse and fine recycled concrete aggregates. The results indicate that the Slump Loss of the recycled aggregate concrete with fly ash was reduced to lower than that of the recycled aggregate concrete without fly ash when the fineness of the fly ash was increased, which increased the Slump Loss of the fresh concrete. Fly ash can be used to increase the compressive strength of recycled aggregate concrete, depending on its fineness and the degree of fly ash replacement. The addition of fly ash with different fineness in recycled aggregate concrete had no significant effect on the splitting tensile strength and the modulus of elasticity of the recycled aggregate concrete, which are related to its compressive strength.

  • use of high fineness of fly ash to improve properties of recycled aggregate concrete
    Journal of Materials in Civil Engineering, 2010
    Co-Authors: Weerachart Tangchirapat, Rak Buranasing, Chai Jaturapitakkul
    Abstract:

    This study used high fineness of fly ash as a cement replacement to improve recycled aggregate concrete properties. The mixture proportions of recycled aggregate concretes were first prepared using 100% recycled coarse aggregate, and then river sand was replaced with recycled fine aggregate at 0, 50, and 100% by weight of the fine aggregate (river sand plus recycled fine aggregate). Results indicated that use of 35–50% fly ash (with respect to total cementitious content) of high fineness could improve Slump Loss behavior in recycled aggregate concretes. Greater proportions of recycled fine aggregates decreased the compressive strength of concrete. However, use of high fineness of fly ash (1.2% retained on a No. 325 sieve) in recycled aggregate concrete could produce greater compressive strength than that of the recycled aggregate concrete alone. The splitting tensile strength of the recycled aggregate concretes containing high fineness of fly ash was 8.2% of its compressive strength, slightly lower than that of the normal aggregate concrete. The modulus of elasticity of recycled aggregate concrete, with or without high fineness of fly ash, was lower than that of the normal aggregate concrete and about 5.9% lower than the value predicted by ACI 318. The results suggest that high fineness of fly ash can be used to improve various properties of recycled aggregate concrete.

  • influence of rice husk bark ash on mechanical properties of concrete containing high amount of recycled aggregates
    Construction and Building Materials, 2008
    Co-Authors: Weerachart Tangchirapat, Chai Jaturapitakkul, Rak Buranasing, Prinya Chindaprasirt
    Abstract:

    Abstract In this study, ground rice husk–bark ash (RHBA) was used as a pozzolanic material in concrete containing high amount of recycled aggregates. The concretes were prepared by using 100% of recycled coarse aggregate (RCA), then river sand was replaced by recycled fine aggregate (RFA) at 0%, 50%, and 100% by weight of the fine aggregate (river sand plus recycled fine aggregate). The results revealed that recycled aggregate concretes had lower compressive strength than that of the conventional concrete (concrete made from normal aggregates). In addition, the use of ground RHBA in recycled aggregate concrete gave higher compressive strength than the recycled aggregate concrete without ground RHBA even though it increased the Slump Loss of concrete. The splitting tensile strength of the recycled aggregate concrete was 8.15% of the compressive strength. Finally, the modulus of elasticity of recycled aggregate concrete was lower than that of the conventional concrete and was about 4% lower than the value predicted by ACI 318.

Keunhyeok Yang - One of the best experts on this subject based on the ideXlab platform.

  • effect of water binder ratio on the mechanical properties of calcium hydroxide based alkali activated slag concrete
    Construction and Building Materials, 2012
    Co-Authors: Keunhyeok Yang, Ahram Cho, Jinkyu Song
    Abstract:

    This paper presents mechanical properties of calcium hydroxide (Ca(OH)2)-activated ground granulated blast-furnace slag (GGBS) concrete with different auxiliary activators in order to provide basic data for developing the mixing procedure and design models for structural concrete. Twelve concrete mixes were prepared with the main parameters of water–binder (W/B) ratio. The measured mechanical properties were compared, wherever possible, with design equations specified in ordinary Portland cement (OPC) concrete code provisions. The investigated Ca(OH)2-based AA GGBS concrete showed an enhanced workability, delayed Slump Loss and similar increasing rate of compressive strength against W/B ratio to that observed in OPC concrete. Similarly to OPC concrete, mechanical properties of Ca(OH)2-based AA GGBS concrete could be expressed as a power function of compressive strength (fc′). The values of the power in the determined equations could be approximately set to be 0.5 for modulus of elasticity, 0.65 for modulus of rupture, tensile strength and direct shear strength, and 0.75 for bond strength. Overall, the present test results revealed that the tested Ca(OH)2-based AA GGBS concrete has a considerable potential for practical application to structural concrete when the W/B ratio is lower than 30%.

  • influence of type and replacement level of recycled aggregates on concrete properties
    Aci Materials Journal, 2008
    Co-Authors: Keunhyeok Yang, Heonsoo Chung, Ashraf F Ashour
    Abstract:

    The study reports results of tests, using only natural aggregates, of a control concrete and nine recycled aggregate concretes. The recycled aggregates were classified according to measured specific gravity and water absorption into three different types, namely: RS II for recycled fine aggregate having 2.36 specific gravity and 5.4% water absorption; RG III for recycled coarse aggregate having a 2.4 specific gravity and 6.2% water absorption; and RG I for recycled coarse aggregate having a 2.53 specific gravity and 1.9% water absorption. Both recycled coarse and fine aggregate replacement levels in separate mixtures were 30, 50, and 100%. For fresh concrete, Slump Loss and bleeding amount with time were recorded. For hardened concrete, there was also measurement of unrestrained shrinkage strain, moduli of rupture and elasticity, and compressive and tensile strengths. Fresh and hardened concrete properties tested, together with a literature-reported comprehensive database, were evaluated with respect to relative aggregate water absorption combined with recycled aggregate quality and volume. Hardened concrete properties, in addition, with different recycled aggregate replacement levels and quality were compared with ACI 318-05 design equation and empirical equality for natural aggregate concrete proposed by Oluokun, whenever possible. That the properties of recycled aggregate-containing fresh and hardened concrete were dependent on the aggregate relative water absorption was clearly shown in test results. In addition, the moduli of recycled aggregate concrete rupture and elasticity was lower than ACI 318-05-specified design equation, when relative aggregate water absorption is respectively above 2.5% and 3.0%.

  • application of powdered superplasticizer to improve of Slump Loss rate in recycled aggregate concrete
    Journal of The Korea Concrete Institute, 2006
    Co-Authors: Keunhyeok Yang, Jaeil Sim, Jaesam Lee, Heonsoo Chung
    Abstract:

    In this study, powered superplasticizer(PSP) agents to improve the Slump Loss rate of recycled aggregate concrete were developed. To evaluate the variation of fluidity against elapsed time and the mechanical properties, twenty four specimens whose main variables had the mixing condition of aggregates, such as natural and recycled gravels, and natural and recycled fine aggregates, were tested. The concrete Slump with a liquid superplasticizer greatly decreased against the elapsed time and dropped by less than 50% of initial Slump after two hours. However the concrete Slump with the PSP agents hardly varied until after half an hour and maintained more than 85% of initial Slump even after an hour. Also the PSP agents made the compressive, splitting tensile, and flexural strength of concrete increased and the shrinkage strain decreased. Considering the properties improvement of concrete, it can be recommended that optimum mixing amount of the PSP agents should be 5% of the amount of cement.

Shicong Kou - One of the best experts on this subject based on the ideXlab platform.

  • properties of concrete prepared with pva impregnated recycled concrete aggregates
    Cement & Concrete Composites, 2010
    Co-Authors: Shicong Kou, Chi Sun Poon
    Abstract:

    This paper reports an experimental study to improve the properties of recycled concrete aggregates (RCA) by their impregnation with polyvinyl alcohol (PVA). The effects of PVA on the development of strength and durability properties of the recycled aggregate concrete were evaluated. The experimental investigation was conducted in two parts. Firstly, the optimal concentration of PVA solution required to improve the recycled aggregates was determined. The RCA was soaked in 6%, 8%, 10%, 12% PVA solutions, and impregnation was conducted under a controlled laboratory environment. Density, crushing value (10% fines value), and water absorption of the PVA impregnated RCA (PI-RCA) were determined. Secondly, the Slump, Slump Loss, compressive and tensile splitting strength, dimensional change (shrinkage) and chloride penetrability of the concretes prepared with the RCA that had been impregnated with the optimal (10%) PVA concentration were determined. It was found that the 10% fines value of the PI-RCA was higher, and the water absorption of the PI-RCA were lower when compared to the untreated RCA. The results show that there was not only an improvement in the mechanical properties of the concrete made with PI-RCA, but also the shrinkage of PI-RCA decreased while the resistance to chloride-ion penetration of the concrete produced increased.

  • influence of moisture states of natural and recycled aggregates on the Slump and compressive strength of concrete
    Cement and Concrete Research, 2004
    Co-Authors: Chi Sun Poon, Z H Shui, L Lam, H Fok, Shicong Kou
    Abstract:

    The influence of moisture states of natural and recycled aggregates on the properties of fresh and hardened concretes was investigated. Concrete mixes were prepared with natural and recycled aggregates at different proportions. The moisture states of the aggregates were controlled at air-dried (AD), oven-dried (OD) and saturated surface-dried (SSD) states prior to use. The ratio of cement to free water was kept constant for all of the mixes. At the fresh state, the Slump Loss for various concrete mixtures was determined, while the compressive strength was determined after curing for 3, 7 and 28 days. The test results showed that the initial Slump values of the concrete mixtures were dependent on the initial free water contents, and the Slump Loss values of the mixtures were related to the moisture states of the aggregates. Slump Loss was significant when 100% AD or OD recycled aggregate was used. The effect of the moisture states of the aggregates on the strength of the concretes prepared with OD and SSD state aggregates at early age (i.e., 3 and 7 days) was noticeable. The concrete prepared with the AD aggregates achieved the highest average strength values at 3, 7 and 28 days. However, at 28 days, the concrete strengths prepared with different types of aggregates were similar. The results suggested that an AD aggregate that contains not more than 50% recycled aggregate is optimum for producing normal strength recycled aggregate concrete.

Jay Gnananandan Sanjayan - One of the best experts on this subject based on the ideXlab platform.

  • Workability and mechanical properties of alkali activated slag concrete
    Cement and Concrete Research, 1999
    Co-Authors: F. G. Collins, Jay Gnananandan Sanjayan
    Abstract:

    This paper reports the results of an investigation on concrete containing alkali activated slag (AAS) as the binder, with emphasis on achievement of reasonable workability and equivalent one-day strength to portland cement concrete at normal curing temperatures. Two types of activators were used: sodium hydroxide in combination with sodium carbonate and sodium silicate in combination with hydrated lime. The fresh concrete properties reported include Slump and Slump Loss, air content, and bleed. Mechanical properties of AAS concrete, including compressive strength, elastic modulus, flexural strength, drying shrinkage, and creep are contrasted with those of portland cement concrete.

Chai Jaturapitakkul - One of the best experts on this subject based on the ideXlab platform.

  • influence of fly ash on Slump Loss and strength of concrete fully incorporating recycled concrete aggregates
    Journal of Materials in Civil Engineering, 2013
    Co-Authors: Weerachart Tangchirapat, Rak Buranasing, Chaiyanunt Rattanashotinunt, Chai Jaturapitakkul
    Abstract:

    This paper investigates the effects of fineness and replacement of fly ash on the fresh and hardened properties of recycled aggregate concrete. Two groups of recycled aggregate concretes were studied and compared with that of conventional concrete (CON) in which crushed limestone and local river sand were used as aggregates. The first group was prepared using 100% coarse recycled concrete aggregate and local river sand. For the second group, crushed limestone and local river sand were fully replaced by both coarse and fine recycled concrete aggregates. The results indicate that the Slump Loss of the recycled aggregate concrete with fly ash was reduced to lower than that of the recycled aggregate concrete without fly ash when the fineness of the fly ash was increased, which increased the Slump Loss of the fresh concrete. Fly ash can be used to increase the compressive strength of recycled aggregate concrete, depending on its fineness and the degree of fly ash replacement. The addition of fly ash with different fineness in recycled aggregate concrete had no significant effect on the splitting tensile strength and the modulus of elasticity of the recycled aggregate concrete, which are related to its compressive strength.

  • use of high fineness of fly ash to improve properties of recycled aggregate concrete
    Journal of Materials in Civil Engineering, 2010
    Co-Authors: Weerachart Tangchirapat, Rak Buranasing, Chai Jaturapitakkul
    Abstract:

    This study used high fineness of fly ash as a cement replacement to improve recycled aggregate concrete properties. The mixture proportions of recycled aggregate concretes were first prepared using 100% recycled coarse aggregate, and then river sand was replaced with recycled fine aggregate at 0, 50, and 100% by weight of the fine aggregate (river sand plus recycled fine aggregate). Results indicated that use of 35–50% fly ash (with respect to total cementitious content) of high fineness could improve Slump Loss behavior in recycled aggregate concretes. Greater proportions of recycled fine aggregates decreased the compressive strength of concrete. However, use of high fineness of fly ash (1.2% retained on a No. 325 sieve) in recycled aggregate concrete could produce greater compressive strength than that of the recycled aggregate concrete alone. The splitting tensile strength of the recycled aggregate concretes containing high fineness of fly ash was 8.2% of its compressive strength, slightly lower than that of the normal aggregate concrete. The modulus of elasticity of recycled aggregate concrete, with or without high fineness of fly ash, was lower than that of the normal aggregate concrete and about 5.9% lower than the value predicted by ACI 318. The results suggest that high fineness of fly ash can be used to improve various properties of recycled aggregate concrete.

  • influence of rice husk bark ash on mechanical properties of concrete containing high amount of recycled aggregates
    Construction and Building Materials, 2008
    Co-Authors: Weerachart Tangchirapat, Chai Jaturapitakkul, Rak Buranasing, Prinya Chindaprasirt
    Abstract:

    Abstract In this study, ground rice husk–bark ash (RHBA) was used as a pozzolanic material in concrete containing high amount of recycled aggregates. The concretes were prepared by using 100% of recycled coarse aggregate (RCA), then river sand was replaced by recycled fine aggregate (RFA) at 0%, 50%, and 100% by weight of the fine aggregate (river sand plus recycled fine aggregate). The results revealed that recycled aggregate concretes had lower compressive strength than that of the conventional concrete (concrete made from normal aggregates). In addition, the use of ground RHBA in recycled aggregate concrete gave higher compressive strength than the recycled aggregate concrete without ground RHBA even though it increased the Slump Loss of concrete. The splitting tensile strength of the recycled aggregate concrete was 8.15% of the compressive strength. Finally, the modulus of elasticity of recycled aggregate concrete was lower than that of the conventional concrete and was about 4% lower than the value predicted by ACI 318.