ABSTRACT
A total of 21 dry concrete mixtures were prepared for testing in this investigation. Two variables were selected, namely sawdust and nano-silica as a partial replacement by volume to fine aggregate and cement, respectively. Seven replacement percentages of sawdust (0%, 5%, 10%, 15%, 20%, 25% and 30%) and three replacement percentages of nano-silica (0%, 5% and 10%) were considered to study the effects of coating sawdust particles with nano-silica on the hardened properties of the sawdust concrete or sawdust-crete. Table 1 presents the mixture ratio proportions by volume. The main mixture ratio is 1 (cement):1 (coarse aggregate):2 (fine aggregate), while the water content required
1 INTRODUCTION
Construction industry is facing a challenge of integrating sustainability in its production development, by either preserving the natural raw materials or reducing CO2 emission (Torkaman et al. 2014). One of the possible ways to achieve this goal is to include waste materials in concrete mixture production (Mohammed et al. 2012 and Mohammed & Fang 2011). Sawdust is an industrial by-product waste from sawmill and continues to increase due to the growing demand on wood products. To reduce pollution due to sawdust combustion, sawdust has been used in concrete mixtures as a partial replacement to fine aggregate by volume (Mohammed et al. 2014). It has been reported that concrete containing sawdust is lighter in weight and exhibits lower thermal conductivity in comparison with normal concrete (Mohammed et al. 2014). However, the adverse effect of the inclusion of sawdust in concrete as a partial replacement to fine aggregate is the reduction in strengths. Therefore, researchers have suggested the treatment of wood waste before inclusion in concrete to enhance bonding between wood waste surfaces and the cement matrix (Coatanlem et al. 2006). Coatanlem et al. (2006) reported an improvement in the strength of concrete containing wood chippings by soaking these chippings in sodium silicate solution prior to mixing in concrete. This led to the improvement of the bond between the wood waste and the cement matrix due to the development of ettringite needles at surfaces of the wood waste and near surface of the cement matrix. Nano-silica (SiO2) has been widely used to improve the concrete properties due to its high reactivity,
for each dry mixture is 8% of the total batch dry weight. Four tests were performed on the samples from selected mixtures for 28 days, which include: compressive strength, Scanning Electron Microscopy (SEM), thermal conductivity test and Mercury Intrusion Porosimetry (MIP). In the mixing process, 2% of water in the total mixture was added to sawdust and mixed with nano-silica for about 5 minutes, and then cement, flay ash, fine aggregate, coarse aggregate and the remaining amount of water were added and the mixing was continued for another 5 minutes. All tests specimens were prepared under compaction pressure, whereas the materials were cast inside the mold in three equal depth layers with 25 blows for each layer and cured in the laboratory environment for 28 days before testing.
