The Experts below are selected from a list of 15981 Experts worldwide ranked by ideXlab platform
M G Alexander - One of the best experts on this subject based on the ideXlab platform.
-
effect of supplementary cementitious materials Binder Type on the pore solution chemistry and the corrosion of steel in alkaline environments
Cement and Concrete Research, 2016Co-Authors: Allan Scott, M G AlexanderAbstract:Abstract The pore solution compositions of paste samples produced with Ordinary Portland Cement (PC), slag 25%, 50% and 75%, fly ash 30%, condensed silica fume (SF) 7%, and a ternary blend of 50% PC, 43% slag and 7% SF were determined. Not only are there significant variations in the concentration of the major cations and anions but also, and equally important from the perspective of development of the passivity of steel in solution, in the level of dissolved oxygen and redox potential. Further, the impact of changes in the pore solution chemistry of cement pastes with SCMs on the passivation and corrosion of steel was investigated with mild steel in simulated pore solutions (SPS). Sulphides and thiosulphates, typically found in slag bearing pastes, appeared to reduce the chloride threshold concentration and increase the rate of corrosion in SPS, which has potential implication for the long term performance of reinforced concrete structures.
-
chloride induced corrosion of steel in cracked concrete part ii corrosion rate prediction models
Cement and Concrete Research, 2016Co-Authors: Mike Otieno, H Beushausen, M G AlexanderAbstract:Chloride-induced corrosion rate (i sub corr) prediction models for reinforced concrete (RC) structures in the marine tidal zone that incorporate the influence of crack width (w sub cr), cover (c) and concrete quality are proposed. Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in the tidal zone. Experimental variables were w sub cr (0, incipient crack, 0.4, 0.7 mm), c (20, 40 mm), Binder Type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). The two proposed models (one each for accelerated and natural i sub corr) can aid not only in quantifying the propagation phase, but also provide a novel way to select c, w sub cr and concrete quality.
-
chloride induced corrosion of steel in cracked concrete part i experimental studies under accelerated and natural marine environments
Cement and Concrete Research, 2016Co-Authors: M Otieno, H Beushausen, M G AlexanderAbstract:Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in a marine tidal zone. Experimental variables were crack width w sub cr (0, incipient crack, 0.4, 0.7 mm), cover c (20, 40 mm), Binder Type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). Results show that corrosion rate (i sub corr) was affected by the experimental variables in the following manner: i sub corr increased with increase in crack width, and decreased with increase in concrete quality and cover depth. The results also show that the corrosion performance of concretes in the field under natural corrosion cannot be inferred from its performance in the laboratory under accelerated corrosion. Other factors such as corrosion process should be taken into account.
-
durability performance of a range of marine concretes and the applicability of the south african service life prediction model
Materials and Structures, 2012Co-Authors: Kung'u Githachuri, M G Alexander, Pilate MoyoAbstract:The paper describes a study that examined and compared the potential durability performance of various geographically distinct South African marine concrete mix Types. Mix proportions were designed at two water/Binder ratios (0.40 and 0.55) for different material combinations of Binder and aggregate Types. Sampling was done at 28, 91 and 182 days. Durability performance was inferred from durability index (DI) tests that measure the resistance of concrete to ion, gas and fluid penetration. Comparison was made on the basis of regional concrete Type, w/b ratio and mix constituents (Binder and aggregate Type). All the concrete mixes were further compared to plain CEM I control concrete mixes at each w/b ratio. Results indicate that low w/b ratio and blended Binder concrete mixes have low penetrability characteristics. Aggregate Type was seen not to have an appreciable influence on the transport properties of concrete. Across the range of geographically different mixes, it was found that with a given concrete grade and Binder Type, marine concrete mixes are practically comparable. This permits the existing Service Life Prediction Model to be more confidently applied for all marine zones in South Africa with possible application in other geographic regions following further research.
-
corrosion in cracked and uncracked concrete influence of crack width concrete quality and crack reopening
Magazine of Concrete Research, 2010Co-Authors: M Otieno, M G Alexander, H BeushausenAbstract:Cracks influence the durability of reinforced concrete (RC) structures in aggressive environments by accelerating the ingress of corrosive agents to the embedded steel. This study investigated the influence of crack width (0·7 mm, 0·4 mm and incipient cracks), Binder Type (100% CEM I (ordinary Portland cement – OPC) and 50/50 OPC/Corex slag blend), water-to-Binder (w/b) ratio (0·40 and 0·55) and crack reopening on chloride-induced corrosion in RC specimens with constant cover of 40 mm. Over the study period (31 weeks), corrosion rates varied from passive values of 0·01 μA/cm2 to active values of 1·50 μA/cm2. Results indicate that corrosion rate is sensitive to crack width, concrete quality (i.e. Binder Type and w/b ratio) and crack reopening. For a given Binder Type and w/b ratio, corrosion rate increased with increasing crack width; however, this increase was smaller in Corex slag specimens (increases of 40% or more) than in OPC specimens (increases 210% or more). Corex slag specimens generally had lower...
Sara Pavia - One of the best experts on this subject based on the ideXlab platform.
-
moisture transfer and thermal properties of hemp lime concretes
Construction and Building Materials, 2014Co-Authors: Rosanne Walker, Sara PaviaAbstract:Abstract Lime–hemp concrete is a low-embodied energy, carbon-negative, sustainable construction material made with a lime-based Binder and hemp aggregate. This work investigates moisture and thermal properties of hemp concretes made with hydrated lime and pozzolans, and those including hydraulic lime and cement. The paper concludes that the Type of Binder influences capillary action of hemp concrete and that increasing the hydraulicity of the Binder, as well as adding a water retainer, reduces capillary absorption. The impact of the Binder Type on permeability is less evident, and the results indicate that the large interparticular spaces between hemp particles (macropores) contribute to permeability to a greater extent than micropores (which are influenced by the hydraulicity of the Binder). Finally, the Binder Type did not have a statistically significant impact on either thermal conductivity or specific heat capacity. A trend however suggests that increasing the Binder’s hydraulic content reduces thermal conductivity and increases heat capacity; and that the presence of water retainers enhances both conductivity and heat capacity.
-
mechanical properties and durability of hemp lime concretes
Construction and Building Materials, 2014Co-Authors: Rosanne Walker, Sara Pavia, Ralph MitchellAbstract:Abstract Hemp-lime concrete is a sustainable and carbon negative construction material. This paper investigates the effect of Binder Type on mechanical strength and durability (resistance to freeze–thaw, salt exposure and biodeterioration). It compares hemp-lime concretes made with a hydrated lime and pozzolan Binder to those including hydraulic lime and cement. SEM analysis revealed abundant hydrates at the hemp interface of the strongly hydraulic commercial Binder while the lime:pozzolan Binders were mostly carbonated. Increasing Binder hydraulicity enhances early strength development however, all concretes achieved similar compressive strengths at 1 year irrespective of the Binder Type. The concretes with lime:pozzolan Binders are more sensitive to freeze:thaw action than those with more hydraulic Binders. Salt exposure resulted in the precipitation of salt layers in the concrete however, this did not have a detrimental impact on the compressive strength of the concrete at 1 year. The results evidenced that hemp concrete is resistant to biodeterioration (7 month exposure). Finally, the addition of water retainer improved the early strength development and freeze:thaw resistance of the concrete with lime–pozzolan Binder.
Rosanne Walker - One of the best experts on this subject based on the ideXlab platform.
-
moisture transfer and thermal properties of hemp lime concretes
Construction and Building Materials, 2014Co-Authors: Rosanne Walker, Sara PaviaAbstract:Abstract Lime–hemp concrete is a low-embodied energy, carbon-negative, sustainable construction material made with a lime-based Binder and hemp aggregate. This work investigates moisture and thermal properties of hemp concretes made with hydrated lime and pozzolans, and those including hydraulic lime and cement. The paper concludes that the Type of Binder influences capillary action of hemp concrete and that increasing the hydraulicity of the Binder, as well as adding a water retainer, reduces capillary absorption. The impact of the Binder Type on permeability is less evident, and the results indicate that the large interparticular spaces between hemp particles (macropores) contribute to permeability to a greater extent than micropores (which are influenced by the hydraulicity of the Binder). Finally, the Binder Type did not have a statistically significant impact on either thermal conductivity or specific heat capacity. A trend however suggests that increasing the Binder’s hydraulic content reduces thermal conductivity and increases heat capacity; and that the presence of water retainers enhances both conductivity and heat capacity.
-
mechanical properties and durability of hemp lime concretes
Construction and Building Materials, 2014Co-Authors: Rosanne Walker, Sara Pavia, Ralph MitchellAbstract:Abstract Hemp-lime concrete is a sustainable and carbon negative construction material. This paper investigates the effect of Binder Type on mechanical strength and durability (resistance to freeze–thaw, salt exposure and biodeterioration). It compares hemp-lime concretes made with a hydrated lime and pozzolan Binder to those including hydraulic lime and cement. SEM analysis revealed abundant hydrates at the hemp interface of the strongly hydraulic commercial Binder while the lime:pozzolan Binders were mostly carbonated. Increasing Binder hydraulicity enhances early strength development however, all concretes achieved similar compressive strengths at 1 year irrespective of the Binder Type. The concretes with lime:pozzolan Binders are more sensitive to freeze:thaw action than those with more hydraulic Binders. Salt exposure resulted in the precipitation of salt layers in the concrete however, this did not have a detrimental impact on the compressive strength of the concrete at 1 year. The results evidenced that hemp concrete is resistant to biodeterioration (7 month exposure). Finally, the addition of water retainer improved the early strength development and freeze:thaw resistance of the concrete with lime–pozzolan Binder.
Mihai O Marasteanu - One of the best experts on this subject based on the ideXlab platform.
-
effect of factors affecting fracture energy of asphalt concrete at low temperature
Road Materials and Pavement Design, 2008Co-Authors: Xinjun Li, William G Buttlar, Andrew Braham, Mihai O Marasteanu, Christopher R WilliamsAbstract:ABSTRACT Low temperature cracking is considered one of the primary distress modes of asphalt pavements built in northern climates. The detrimental effects of low-temperature cracking of asphalt pavements have motivated new work in fracture testing of hot-mix asphalt (HMA). A comprehensive study was conducted to investigate the effect of various factors on the fracture resistance of asphalt mixtures at low temperatures. The Semi-Circular Bending (SCB) and Disc-Shaped Compact Tension Test (DCT) fracture tests were performed at three low temperatures to measure the fracture energy for 28 asphalt mixtures, which represent a combination of factors including Binder Type, Binder modifier, aggregate Type, asphalt content and air voids. In this study, the analysis from the experimental data indicates that fracture energy is strongly dependent upon temperature and significantly affected by Type of aggregate and Binder modifier. The results of the analysis show the significance of air voids in the SCB test, but no s...
-
effect of Binder Type aggregate and mixture composition on fracture energy of hot mix asphalt in cold climates
Transportation Research Record, 2007Co-Authors: Andrew Braham, William G Buttlar, Mihai O MarasteanuAbstract:Detrimental effects of low-temperature cracking of asphalt pavements and overlays have motivated new work in fracture testing of hot-mix asphalt (HMA). Recent work has indicated that the fracture behavior of asphalt concrete at low temperatures can be accurately predicted with a testing and modeling system that, along with viscoelastic bulk material properties, relies simply on fracture energy and material strength. In this study, the disk-shaped compact tension test is used to measure fracture energy of 28 HMA mixtures designed for cold climates. Four parameters are investigated: aggregate Type (limestone and granite), temperature (three temperatures, encompassing the Superpave® performance graded Binder low temperature grade for each Binder tested), asphalt content (Superpave design asphalt content and Superpave design content plus 0.5%), and air voids (4% and 7%). A statistical analysis of results demonstrates the significance for fracture energy of Binder content at higher temperatures, aggregate Type...
Adriana Martinez - One of the best experts on this subject based on the ideXlab platform.
-
effect of the recycling process and Binder Type on bituminous mixtures with 100 reclaimed asphalt pavement
Construction and Building Materials, 2018Co-Authors: Adria Nosetti, Domingo Perezmadrigal, Feli Perezjimenez, Adriana MartinezAbstract:Abstract There is a great interest in increasing the amount of recycled material used in asphalt mixes because of the beneficial impact on the environment. This is leading to the development of different recycling procedures, from cold in-situ to hot in-plant recycling. The objective of the study presented in this paper is to evaluate cracking resistance of recycled mixes manufactured by three Types of processes, i.e., cold with emulsion, hot with high penetration bitumens and hot with emulsion (half-warm mixture), using 100% of reclaimed asphalt pavement (RAP) at different temperatures. Differences in their workability and ease of use are also analysed by gyratory compaction.