Abstract

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.

Introduction

The negative impact of cement in concrete on the environment has aroused the need for an alternative solution by using SCM to produce low carbon concrete. Result from literatures indicates that the performance of low carbon concrete is influenced by the type of SCM materials used as well as the percent cement replacement. Guidelines and procedures on the dosage of SCM for effectiveness in low carbon concrete requires that careful selection of materials be carried out with the use of systematic reviews and meta-analysis. The efficacy of research interventions with the use of systematic reviews and meta-analysis to establish guidelines in clinical practice has been demonstrated in the health care [1]. The 2050 Roadmap developed by the international Energy Agency and World Business Council for Sustainable Development considered reduction in rise of global warming to 2 degrees through the reduction of carbon emissions. This implies that emissions from cement manufacture should be reduced by 2050 compared to its current level in view of global energy demand between 12 and 23%. To attain the 2050 target, the use of waste materials as SCM is emphasized for low carbon concrete production [2,3]. In view of the role of concrete for the implementation of United Nation sustainable Development Goals (SDGs) for sustainable housing, there has been a surge in the interest of researchers for sustainable concrete which made it necessary for a thorough and careful application of evidence-based materials selection for cost effectiveness and sustainability [4,5]. These myriads of research are conducted across locations with different methods, materials and at some point, occurring at the same time which could induce repetition, bias, and lack of updated information on the status of an intervention. For this reason, other field of study encourages collaboration and synergy in the form of protocol registration. This is evident in the field of medicine with the Cochrane Collaboration and in social welfare, education, crime, and justice with the Campbell reviews [6,7]. Such collaboration is not seen in the areas of concrete research considering that concrete is the second most used materials after water [8] and its place in addressing vision 2050 target for zero carbon emissions [9], hence the need for systematic review and meta-analysis of cement replacement materials. Unfolding of a research gap in any field of research is based on the extent to which the previous boundaries of research can be expanded with a view to answer research question. This requires building a solid foundation on the discovered body of knowledge through literatures reviews of existing findings in comparison with similar contextual reviews

Conclusion

The widespread use of agricultural and industrial waste as cement replacement materials has affirmed the viability of emerging alternative cement materials for which potentials can be sustainable and durable. The desire for low carbon concrete evident due to its impact on the environment requires a compressive search owing to the fact the performance of cement in concrete has stand the test of time meeting all set criteria of performance except that of sustainability. Due to the huge demand on sustainable low carbon concrete, the mere performance of concrete in terms of compressive strength is no longer a sufficient metrics to measure its performance hence it has been supplemented using recycle industrial and agricultural waste to account for eco friendliness, economy, and sustainability.

• Mechanical properties of SCMs from industrial waste from same source as shown in the combination of gypsum and PFA exhibit poor performance due to variability in density and mineralogy. The chemical composition of PFA at CaO (24.5%) compared to gypsum at CaO (37.7%) and SiO2(35.2%) for PFA while that of gypsum (4%) presents more of a cementitious material than the latter from which its mechanical strength is based. As the cementitious properties of SCMs is dependent on high CaO composition and pozzolanic nature exhibited with more of SiO2. The ratio of CaO/SiO for PFA is 0.69 and that of gypsum is 9.425. The performance of the concrete with a blend of PFA and gypsum resulted to performance owing to high CaO/SiO2 ratio which culminated to its poor cementitious composition.