Compliance criteria for quality concrete

With the advancement in cement technology, it is now possible to produce concrete of high strength with increased water/cement ratio. While this may satisfy the strength requirement, it is possible that the durability of such concrete is despaired. Though international organizations specify minimum cementititous materials content and maximum water/cementititous materials ratio, the quality assessment parameter is still the compressive strength. There is, however, a need to switch to permeability or chloride diffusion indices to ascertain the quality concrete. At the same time, compliance criteria for the present-day concrete need to be developed. In the reported study, an extensive experimental work was carried out to assess the compressive strength development, depth of water penetration and chloride permeability of plain, silica fume and fly ash cement concretes prepared with varying mixture proportions. The experimental data were utilized to develop statistical relationship between the mixture design parameters and the strength and durability indices. These data were also utilized to develop quality compliance criteria for concrete prepared with the crushed limestone aggregates

Compliance criteria for quality concrete

With the advancement in cement technology, it is now possible to produce concrete of high strength with increased water/cement ratio. While this may satisfy the strength requirement, it is possible that the durability of such concrete is despaired. Though international organizations specify minimum cementititous materials content and maximum water/cementititous materials ratio, the quality assessment parameter is still the compressive strength. There is, however, a need to switch to permeability or chloride diffusion indices to ascertain the quality concrete. At the same time, compliance criteria for the present-day concrete need to be developed. In the reported study, an extensive experimental work was carried out to assess the compressive strength development, depth of water penetration and chloride permeability of plain, silica fume and fly ash cement concretes prepared with varying mixture proportions. The experimental data were utilized to develop statistical relationship between the mixture design parameters and the strength and durability indices. These data were also utilized to develop quality compliance criteria for concrete prepared with the crushed limestone aggregates

PERFORMANCE EVALUATION OF REPAIR MATERIALS

Reduction in the useful service-life of reinforced concrete construction, mainly due to reinforcement corrosion, is a major problem facing the construction industry worldwide, in general, and the Arabian Gulf in particular. Deteriorating structures need to be repaired not only to utilize them for their intended service-life but also to assure the safety and serviceability of the associated components. While several repair materials are used for repair and rehabilitation of the deteriorated concrete structures worldwide, their performance in the Arabian Gulf environment, dominated by the extreme temperatures and aridity, has not been thoroughly investigated. This paper reports the results of a study conducted to evaluate the performance of repair materials available in the local market. Based on the data developed in the study, criteria for the selection of repair materials are recommended

Experimental and modelling of alkali-activated mortar compressive strength using hybrid support vector regression and genetic algorithm

This paper presents the outcome of work conducted to develop models for the prediction of compressive strength (CS) of alkali-activated limestone powder and natural pozzolan mortar (AALNM) using hybrid genetic algorithm (GA) and support vector regression (SVR) algorithm, for the first time. The developed hybrid GA-SVR-CS1, GA-SVR-CS3, and GA-SVR-CS14 models are capable of estimating the one-day, three-day, and 14-day compressive strength, respectively, of AALNM up to 96.64%, 90.84%, and 93.40% degree of accuracy as measured on the basis of correlation coefficient between the measured and estimated values for a set of data that is excluded from training and testing phase of the model development. The developed hybrid GA-SVR-CS28E model estimates the 28-days compressive strength of AALNM using the 14-days strength, it performs better than hybrid GA-SVR-CS28C model, hybrid GA-SVR-CS28B model, hybrid GA-SVR-CS28A model, and hybrid GA-SVR-CS28D model that respectively estimates the 28-day compressive strength using three-day strength, one day-strength, all the descriptors and seven day-strength with performance improvement of 103.51%, 124.47%, 149.94%, and 262.08% on the basis of root mean square error. The outcome of this work will promote the use of environment-friendly concrete with excellent strength and provide effective as well as efficient ways of modeling the compressive strength of concrete

Effect of sodium hydroxide concentration on strength and microstructure of alkali-activated natural pozzolan and limestone powder mortar

The present study evaluates the effect of sodium hydroxide concentrations on strength, bond properties, reaction products and the microstructures of binary blended alkali-activated volcanic natural pozzolan and limestone powder (AANL) mortar. Six AANL mortar were prepared with alkaline activators of 4–14 M NaOH(aq) and Na2SiO3(aq) such that the activators ratio was 1:1. Curing was done at 75 °C for 24 h duration. The maximum 90-day compressive strength of 31.3 MPa was achieved with 10 M NaOH(aq) while 76% of the strength could be achieved within three days when 10 M NaOH was used. The 28-day tensile strength of 2.32 MPa was achieved with 14 M NaOH(aq). XRD characterizations revealed that activation with a strong concentration of sodium hydroxide (10 M NaOH(aq)) led to the formation of anorthite (CaAl2Si2O8) and gehlenite (Ca0.Al2O3SiO2). SEM + EDX indicated that strong alkali (10 M NaOH) enhanced microstructural density compared to that of mild alkali (4 M NaOH(aq))

Effect of NaOH Molarity on the Strength and Microstructure of Natural Pozzolan-Based AAC

Alarming levels of greenhouse gas emissions has triggered change in the mode of direction of building material research. In this pursuit, alkali activated binders (AAB), synthesized by activation of industrial by products and natural materials in the presence of highly alkaline solutions, have offered viable alternative to OPC. However, there are quite a number of variables which controls the properties of these binders. Among these parameters, SS/SH ratio and molarity of sodium hydroxide solution plays a very important role in the development of these binders. Therefore, this research investigates the effect of SS/SH ratio, subsequently, molarity of SH solution on the properties of natural pozzolan based AAB. The NP was activated with sodium silicate to sodium hydroxide ratio (SS/SH) between 2.0 to 2.75. Subsequently, the molarity of SH solution was varied between 8 to 14. The development in strength was monitored on the specimens cured at 60 °C. SEM and EDS techniques were used to determine the nature of the binder formed during alkali activation. The results have shown that SS/SH ratio of 2.5 and 14 molar SH solution resulted in higher strength and finer microstructure as compared to others. Also, it was understood that there exists a suitable silica modulus of combined activator which results in higher polymerization

Effect of NaOH Molarity on the Strength and Microstructure of Natural Pozzolan-Based AAC

Alarming levels of greenhouse gas emissions has triggered change in the mode of direction of building material research. In this pursuit, alkali activated binders (AAB), synthesized by activation of industrial by products and natural materials in the presence of highly alkaline solutions, have offered viable alternative to OPC. However, there are quite a number of variables which controls the properties of these binders. Among these parameters, SS/SH ratio and molarity of sodium hydroxide solution plays a very important role in the development of these binders. Therefore, this research investigates the effect of SS/SH ratio, subsequently, molarity of SH solution on the properties of natural pozzolan based AAB. The NP was activated with sodium silicate to sodium hydroxide ratio (SS/SH) between 2.0 to 2.75. Subsequently, the molarity of SH solution was varied between 8 to 14. The development in strength was monitored on the specimens cured at 60 °C. SEM and EDS techniques were used to determine the nature of the binder formed during alkali activation. The results have shown that SS/SH ratio of 2.5 and 14 molar SH solution resulted in higher strength and finer microstructure as compared to others. Also, it was understood that there exists a suitable silica modulus of combined activator which results in higher polymerization