Development of low carbon concrete and prospective of geopolymer concrete using lightweight coarse aggregate and cement replacement materials

The use of Ground Granulated Blast-furnace Slag (GGBS) as an alternative cement replacement material incombination with conventional coarse aggregate have been successful in the production of near green concrete.Undoubtedly, GGBS has exhibited good cementitious attributes, however, there are concerns with slow strengthdevelopment and workability owing to its non-pozzolanic activities as well as some degree of porositynotwithstanding the sustainability potential. Therefore, this study presents a lytag based geopolymer lightweightconcrete with high strength development, improved mechanical properties and reduced embodied carbon. Tofurther improve and enhance the potential production of green concrete, complete replacement of conventionalcoarse aggregate with a recycled lightweight aggregate from industrial waste was carried out. The geopolymerprecursors consisted of sodium hydroxide, sodium silicate, GGBS and silica fume to optimize the performance ofthe concrete at 60–80% cement replacement for a target design mix of 20, 30, 40, and 50 MPa. The performanceof lytag based geopolymer concrete was compared with that of non-geopolymer lytag based concrete (controlsamples). The results show a 42% increase in compressive strength for the geopolymer lightweight concrete anda 22% increase in ultimate compressive strain which is an indication of improved moment of resistance instructural design. The results also show a 46–61% reduction in embodied carbon for the use of non-geopolymerlytag based concrete and 69–77% reduction for lytag based geopolymer concrete. The geopolymer concretebetween 7 and 63 days of loading increases by 0.55% in creep strain compared with increases of 2.81% for non-geopolymerlytag based concrete and reduction to 27.96% for the normal weight concrete. Modulus of Elasticityreduces with age of loading for the geopolymer concrete during creep at 0.39% compared to reduction of 1.93%for non-geopolymer lytag based concrete and increase of 12% for the normal weight concrete

Mapping and synthesizing the viability of cement replacement materials via a systematic review and meta-analysis

Supplementary cementitious materials (SCM) are alternative to the conventional cement and have been studied by so many authors owing to the high carbon content of cement. The use of SCM is significant in addressing challenges of carbon emission and its impact on the 2050 carbon reduction RoadMap. Available studies shows that SCM obtained from both industrial and agricultural wastes presents significant variability in performance as cement dosage in concrete increases. The first aim of this study is to map and synthesize the available evidence from literatures to support this variability. The second objective is to provide statistical evidence from available literatures of certain SCM that enhance the structural performance of low carbon concrete in terms of compressive strength. From the results, trend of findings from literatures on the use of SCM shows a surge in research for cement replacement occurring over the last decade with optimal performance for industrial waste SCM shown to be limiting at 40% cement replacement while that from agricultural waste occurs at 10% cement replacement. Data were sourced from Scopus database and selected from peer review journals of both primary and secondary studies on cement replacement materials. 728 published articles were obtained from the search using four strings namely,’Recent cement* replacement and cementitious materials’’, ‘’Recent supplementary cementitious materials’, ‘’Eco-friendly and cementitious materials’’ and ‘’Low carbon intensive cement replacement materials’. Meta-analysis is carried out on the selected articles having quantitative data to synthesise some of the result of the published articles to examine the impact of Ground granular base slag and Pulverized Fuel Ash cement on concrete strength development as cement replacement. It is shown that Ground granular base slag, Pulverized Fuel Ash and Metakaolin improve and enhance the eco friendliness of the concrete. From the results, optimal percentage of cement replacement is a gap which remains unresolved due to mineralogy and reactivity of the SCMs and would provide the solution for the desired green concrete optimization. It is shown with statistical evidence from meta-analysis that ground granular base slag and Pulverised fuel ash decreases the effect of low compressive strength by at least 2% to about 75% which is considered in our opinion as effective to enhance the sustainability of concrete

Evaluation of the structural performance of low carbon concrete

Evaluation of the effect of embodied carbon reduction using an optimized design section for a ground beam, use of supplementary cementitious materials, and replacement of normal aggregatewith light weight aggregate on the mechanical properties of low-carbon concrete was carried out. A creep coefficient of 0.019 was estimated for a 365-day period on a change in section from 1 to 0.6 m2 on a proposed trapezoidal section for ground beam, which showed a negligible difference when compared to the normal rectangular section owing to a reduction in embodied carbon due to the associated reduction in concrete volume and reinforcement. Training of 81 low-carbon concrete data sets in MATLAB using artificial neural network for 100% cement replacement with ground granular base slag indicates good performance with a mean square error of 0.856. From the study, it was observed that the extent of carbonation depth in concrete evidenced the measure of compressivestrength formation based on the specific surface area of the binder and the water absorption rate of the aggregate, while enhancing the flexural strength of the low-carbon concrete required a cement-to supplementary-cementitious-material ratio of 0.8

Optimisation of embodied carbon and compressive strength in low carbon concrete

To improve the prediction of compressive strength and embodied carbon of low carbon concrete using a program algorithm developed in MATLAB, 84 datasets of concrete mix raw materials were used. The influence of water, silica fume and ground granular base slag was found to have a significant impact on the extent of low carbon concrete behaviour in terms of compressive strength and embodied carbon. While the concrete compressive strength for normal concrete increases with reducing water content, it is observed that the low carbon concrete using lightweight aggregate material increases in compressive strength with an increase in embodied carbon. From the result of the analysis, a function was developed that was able to predict the associated embodied carbon of a concrete mix for a given water-to-cement ratio. The use of an alkaline solution is observed to increase the compressive strength of low carbon concrete when used in combination with ground granular base slag and silica fume. It is further shown that ground granular base slag contributes significantly to an increase in the compressive strength of Low carbon concrete when compared with pulverised fly ash. The optimised mix design program resulted in a 26% reduction in embodied carbon and an R 2 value of 0.9 between the measured compressive strength and the opti-mised compressive strength

Development of a Lytag-silica fume based lightweight concrete and corresponding design equation for pure bending

This study presents a novel Lytag-silica fume concrete (LSFC) for structural and other construction applications. The evaluation of compressive strength development and stress strain relationships of the LSFC light weight was carried out to determine the strength growth in LSFC and for the development of the proposed beam design equation. Four different mix compositions were adopted for concrete grade 20, 30, 40, 50 at cement dosage of 260, 330, 450 and 570 kg/m3 on 24 concrete samples. A rectangular parabolic stress block was derived using representative stress-strain curves, and the results show that the parameter kbal that defines the ultimate design moment in the compressive zone was equal to 0.107 compared to kbal value of 0.167 for a normal weight concrete according to Eurocode 2. The ultimate compressive strain obtained for LSFC was 2.18‰ after 28 days for the LSFC compared to that of the normal weight concrete (NWC) of 3.5‰. The result also shows that 94.15 % of the compressive strength of LSFC was developed within 7 days of age due to the high pozzolanic chemical composition of Lytag and Silica fume. A reduction in embodied carbon was evident on reduction in water to cement ratio. The analysis and design results compared with NWC shows that Lytag-silica fume light weight concrete reduces reinforcement to 47 % with an increase in shear resistance. Scanning Electron microscopy analysis shows that the pathology and microstructure of the lytag-silica fume concrete is characterised with high micro pores with increasing water to cement ratio while the low water to cement ratio exhibit low distribution of pores which is an attribute of good mechanical properties of LSFC. The stress strain behaviour does not display a strain softening phenomena which is indicative of good flexural strength

Development of a Lytag-silica fume based lightweight concrete and corresponding design equation for pure bending

This study presents a novel Lytag-silica fume concrete (LSFC) for structural and other construction applications. The evaluation of compressive strength development and stress strain relationships of the LSFC light weight was carried out to determine the strength growth in LSFC and for the development of the proposed beam design equation. Four different mix compositions were adopted for concrete grade 20, 30, 40, 50 at cement dosage of 260, 330, 450 and 570kg/m3 on 24 concrete samples. A rectangular parabolic stress block was derived using representative stress-strain curves, and the results show that the parameter kbal that defines the ultimate design moment in the compressive zone was equal to 0.107 compared to kbal value of 0.167 for a normal weight concrete according to Eurocode 2. The ultimate compressive strain obtained for LSFC was 2.18 ‰ after 28 days for the LSFC compared to that of the normal weight concrete (NWC) of 3.5 ‰. The result also shows that 94.15% of the compressive strength of LSFC was developed within 7 days of age due to the high pozzolanic chemical composition of Lytag and Silica fume. A reduction in embodied carbon was evident on reduction in water to cement ratio. The analysis and design results compared with NWC shows that Lytag-silica fume light weight concrete reduces reinforcement to 47% with an increase in shear resistance. Scanning Electron microscopy analysis shows that the pathology and microstructure of the lytag-silica fume concrete is characterised with high micro pores with increasing water to cement ratio while the low water to cement ratio exhibit low distribution of pores which is an attribute of good mechanical properties of LSFC. The stress strain behaviour does not display a strain softening phenomena which is indicative of good flexural strength