PROPERTIES OF HYBRID FIBERS REINFORCED ENGINEERED GEOPOLYMER COMPOSITE CONTAINING GGBFS AND NON-CONVENTIONAL FLY ASH

Abstract

A multifunctional seismic retrofitting technology is being developed for unreinforced masonry structures. This technology proposes to use lightweight engineered cementitious composites (ECC) trowelling on the surface of the masonry wall to improve its strength, ductility, and thermal performance. As part of research efforts, this thesis is to develop lightweight engineered geopolymer composites (EGC) using locally available industrial by-products and hybrid fibers. A possible alternate for typical engineered cementitious composite (ECC) is the recently developed engineered geopolymer composite (EGC). It is being investigated as a green building material with significant potential to lower CO2 emissions, primarily by the incorporation of industrial by-products into its matrix. As binder materials in EGC, ASTM-classified fly ash and GGBFS are used. In Kazakhstan, tons of waste materials from natural resources are produced including coal fly ash. However, due to the absence of quality control, locally available fly ash has a coarser particle size distribution which resulting in a low strength activity index than the ASTM specification, categorizing it as non-conventional fly ash. It is unclear if such non-conventional fly ash can achieve similar required mechanical properties as the classified one. Thus, it is worthwhile to investigate the suitability of the local fly ash as a binder material in the EGC. Additionally, the high cost of mostly used oil-coated polyvinyl alcohol (PVA) fiber as reinforcement in the ECC and EGC, limits their application in the industry, particularly in developing countries. To investigate the possibility of replacing the PVA fibers with other economically beneficial fibers such as Polypropylene (PP) fibers and steel (S), the EGC with different fiber combinations is considered in this thesis. Moreover, as part of requirement for multifunctional retrofitting, this thesis investigates the possibility for replacing the fine sand with lightweight aggregates (e.g. hollow micro glass bubbles (HMGB)) in the EGC in order to improve its thermal performance. This thesis investigates the workability, dry shrinkage, compressive strength, tensile strength, stain hardening capacity and thermal conductivity for the proposed EGC through extensive experimental studies. The investigation was conducted in two studies. In study I, the EGC containing non-conventional fly ash, GGBFS, and different fibers combinations was studied. The mixture proportion between fly ash and GGBFS was selected from a previous study. The main study parameter is the fiber combination among PVA, PP, and steel with a fixed total fiber content of 2%. Eight different fiber combinations were studied. In study II, the lightweight EGC by replacing the fine sand with the HMGB was studied for selected four

mixtures in study I. The results from Phase I indicates that the EGC with the non-conventional fly ash can achieve required mechanical properties in terms of strength and strain hardening capacity. The EGC with PVA and PP combined fiber can achieve similar mechanical properties as the one with PVA only, while the PVA and steel combination does not perform well. A suitable combination can be 1.5% PVA and 0.5% PP. The highest compressive strength of EGC reaches with this combination and is 25 MPa. However, both tensile strength and strain slightly decrease to 2.04 MPa and 2.03%, respectively. It is also observed that by adding the fiber, the dry shrinkage and long-term strength loss occurred in the matrix have been significantly reduced. The EGC also exhibits lightweight and superior thermal performance as compared to the ECC without introducing lightweight aggregates. The results from Phase II show that replacing the fine sand with HMGB slightly lower the mechanical performance of the EGC. At the same time, it does not significantly reduce the weight and improve the thermal performance. Therefore, it is not necessary to replace the fine sand with the HMGB.