Strength and Durability Properties of Self-Compacting Concrete Incorporating Rice Husk Ash and Metakaolin

Abstract

This study is about design and development of self-compacting concrete (SCC) using supplementary cement materials (SCMs). These SCMs has wide applications in concrete which contribute in enhancement of strength and durability. In this study, two types of SCMs have been used; Metakaolin (MK) and Rice Husk Ash (RHA). MK is a SCM which results from the heating of kaolinite clay in span of specified temperature, while RHA is a by-product obtained from the paddy fields. Rice husk when burnt in range of specified temperatures it results in RHA. To carry out the investigations,firstly, a control mix (M1), without any of the SCM (MK & RHA) was designed. Then, three mixes (M2, M3, M4) were prepared with partial replacement of cement with MK in proportions of 5, 10 and 15%. Three other mixes (M5, M6, M7) were made with the partial replacement of fine aggregates with RHA in the varying proportions of 10, 20 and 30%. Then, on the basis of 28–day compressive strength, ten additional mixes (M8 – M16), with combination of both (MK & RHA) were made. In mixes M8 – M10, MK content was kept constant at 5% & RHA content was varied between 10 to 30%. Similarly, in mixes M11 – M13 & mixes M14 – M16 MK content was kept constant at 10% & 15% respectively, and RHA content was varied between 10 to 30%, similar to mixes M8 – M10. Mixes made with MK and RHA were tested for fresh properties, strength properties (compressive strength and splitting tensile strength), durability properties (water absorption, sulphate resistance, RCPT) and micro-structural properties (SEM and XRD) up to age of 365 days. Statical analysis of the results was also undertaken. All the mixes fulfilled the EFNARC criteria for the fresh properties. Use of MK and RHA increased the water demand but that can be managed by increasing the slight dose of super-plasticizer. The inclusion of MK and RHA positively affected the compressive strength at all ages. Mix M11 (10MK10RHA) showed the highest strength upgradation. It showed 26%, 27%, 42% and 48% increase in strength than the control mix at 7, 28, 90 and 365 days respectively. Also, all other mixes exhibited more strength than the control mix. Similar trends were observed for splitting tensile strength results. The highest strength was achieved by the mix M11 (10MK10RHA), which showed the maximum strength of 2.74, 4.43, 5.12 and 5.96 MPa at 7, 28, 90 and 365 days respectively. It was observed that strength increased up to 10% RHA and after that it starts decreasing, while in case of MK it increases up to 10% and slightly decreases at 15%. The water absorption and porosity for mixes containing MK+RHA was lowered as against the control mix. Inclusion of MK and RHA positively affected water absorption and porosity but at the same time level of water absorption and porosity rises with the increased percentage of MK and RHA. Inclusion of MK and RHA has positive impact on sulphate resistance and RCPT of SCC mixes. All the mixes made with the use MK and RHA had better resistance to sulphate attack as against the control mix. With 15%MK and 10%RHA there was 44%, 74% and 77% decrease in chloride permeability at 28, 90 and 365 days respectively SEM images showed lesser voids and more homogenous structure along with formation of C-S-H gel for the mixes made with MK and RHA. XRD images showed maximum amount of unused Silica for the mix made without MK and RHA, while mixes with MK and RHA had lesser amounts of unused silica. This is the reason for better performances of these mixes. All the test results of SCC mixes were statically analysed and comparatively studied using ‘ANNOVA’ test. The mean values of mixes made with MK and RHA was higher than the control mix for all strength and durability properties. Also, lower bound and upper bound interval was higher for all mixes made with MK and RHA as compared to control mix. The co-relation analysis depicted strong relationship among the various results.