Potential Use of Processed Lateritic Fine Aggregates in Cement Mortars and Concretes for Sustainable Development

Abstract

Availability of river sand is becoming scarce, due to rapid increase in infrastructure projects in India. Acute shortage of river sand, has led to indiscriminate sand mining. Adverse effect of sand mining includes river bank erosion, river bed degradation, loss of biodiversity and deterioration of river water quality and ground water availability. To address the above issues, research efforts are on, to find substitutes for river sand to be used as fine aggregate in mortars and concretes. One among the locally available resources is laterite. Laterite is a product of tropical or sub-tropical weathering, which is an abundant soil material available in many parts of India. An attempt has been made to characterize the processing technique to obtain good quality lateritic fine aggregates (lateritic FA). Experiments were designed and conducted to study the performance of lateritic FA as replacement to river sand, in cement mortars and concretes. Processed lateritic FA in replacement levels of 0, 25, 50, 75 and 100 wt.% to river sand at all fineness levels (Zone I to Zone IV as per Indian standards) is considered. The workability and compressive strength characteristics of cement mortars and concretes are evaluated. Laterized mortars with Zone III and Zone IV fine aggregates, at all replacement levels, result in the same compressive strengths as those of control mortars. Suitable strength enhancement technique has been attempted to achieve strengths of Zone I and Zone II lateritic fine aggregates based mortars at 100 wt.% replacement, to achieve strength at least equal to or more than those of control mortars. Laterized concretes have achieved nearly the same strengths as those of control concretes, at all replacement levels and for all fineness levels (Zone I to Zone IV). Microstructure studies were also conducted to understand the arrangement of river sand and lateritic FA with cement matrix and their Interfacial Transition Zones (ITZ) using Scanning Electron Microscope (SEM). In the second phase, performance evaluation of laterized mortars blended with GGBS and fly ash at elevated temperatures was studied. The study was carried out in three stages, in the first stage effect of elevated temperatures on laterized mortar with different proportions of fly ash and GGBS were evaluated with constant retention period and varying exposure temperature. In the second stage, the best performing laterized mixes with GGBS and fly ash were examined for different retention periods of 30, 60 and 90 minutes. The effect of retention period on the physical and mechanical properties are investigated. In the third stage, the effect of different cooling regimesii on the residual properties of laterized mortar specimens when subjected to elevated temperatures are assessed. In the present study, three cooling regimes namely furnace cooling, ambient air cooling and water quenching were adopted. Microstructure analysis of specimens subjected to different exposure temperatures was done through SEM image analysis using image J software. In the third phase, usage potential of recycled concrete aggregates (RCA) along with lateritic FA in concrete was studied. Mechanical properties of RCA based laterized concretes were examined. Suitable strength enhancement methodology is adopted to overcome the decrement in strength caused by the usage of RCA in concrete. Finally, sustainability in the production of concrete is achieved by using GGBS as sole binder and lateritic FA as fine aggregates and RCA as coarse aggregates along with alkali solution as an activator. The resultant alkali activated slag concrete with lateritic FA and RCA shows almost similar results in terms of mechanical properties when compared to control concrete.