Thermo-Mechanical and Durability Properties of Cement Mortar Integrated With Nano-Silica Particles

Abstract

Evolution of infrastructure investments is important for the alleviation of poverty in emerging countries like India. Consequently, time frame execution of construction projects plays a vital role. This can be achieved through the application of superior pozzolanic material such as nano-silica in cementitious composites. However, there are certain number of problems associated with the inclusion of nano-silica such as workability issue, high heat of hydration, shrinkage and the associated cost. Hence, it is more appropriate to use supplementary cementitious materials (SCMs) in conjunction with nano-silica to produce high performance sustainable cementitious composite mixes. On the other side, the scientific and industrial communities are heavily investing on conservation of energy. Therefore, there is a need to increase the energy efficiency of the building constituents by cutting down the thermal loading. In this regard, various classes of phase change materials (PCMs) act as heat absorbing/transfer medium (latent heat storage system). However, major detriment of PCMs in cementitious composites are its physical and chemical interference with hydration products leading to loss in structural integrity. Therefore, there is a need to incorporate a highly reactive material like nano-silica along with PCM resulting in thermally efficient and sustainable construction material. In this perspective, present study was carried out to understand the influence of nano-silica on hydration properties of binary, ternary and quaternary blended cementitious composites containing micro to nano sized admixtures including fly ash (FA), ultrafine fly ash (UFFA) and colloidal nano-silica (CNS). Study also demonstrated the influence of integrating phase change materials (PCMs) on thermo-mechanical properties of nano-silica admixed cementitious composites. In the initial stage of study dosage of nano-silica (0.5% to 3.5% at 0.5% interval) was replaced with ordinary Portland cement in correspondence to obtain the optimum compressive strength of cement mortar. Further, optimised cementitious mix was designed through particle packing theory by adding suitable proportion of FA and UFFA. In the later part of the experimental investigation, nano-silica modified mix was added with the desired proportion of PCMs to identify the thermal efficiency of the cementitious composite. Hydration, mineralogical and microstructural studies of cementitious composites were carried out through advanced characterization techniques such as, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy empowered with energy dispersive X-ray spectroscopy (SEM-EDX), respectively. Thermal properties of PCM integrated cementitious composites were determined by means of differential scanning calorimetry (DSC). The experimental test results revealed that the optimum dosage of CNS in binary blended cementitious composites was found to be 3%. However, slump flow test indicated the intensified demand for water absorption and reduced workability with increase in level of CNS content. The presence of nano-silica in cementitious system amplified the hydration and pozzolanic activity, thereby promoting densified microstructure. It is to be noted that quaternary blended mix also showed promising results with respect to hydration, microstructure, mechanical and durability properties. Experimental results of PCMs integrated cementitious composites showed improved thermal efficiency as well as reduced the chemical shrinkage, but adversely affected the mechanical, hydration, and durability properties. It was found that cementitious mortar comprising of both nano-silica and PCMs have compensated the drawbacks of one another. Composite mix (having both nano-silica and PCMs) showed superior strength gain at early age, better durability resistance, low chemical shrinkage, and superior thermal performance. At this point of time, it is understood from the experimental investigation that it is possible to attain sustainable cementitious composites by blending fly ash or/and ultrafine fly ash along with highly reactive nano-silica. This experimental study also gives an understanding that PCMs and nano-silica can be combined in cementitious composites to a suitable proportion to give the best performance with respect to the compressive strength development, minimization of shrinkage, hydration, and microstructure development. In addition, a PCM admixed cementitious composite can be proportioned to store a suitable amount of heat energy.