Microorganism is an unique living element and has the ability to precipitate minerals through the process of biomineralisation. The precipitation process occured naturally and most of the precipitated products are very important compound composed of such as carbon, nitrogen, oxygen, sulphur, phosphorus and silica. So far, concrete incorporated with microorganism that able to precipitate calcium carbonate (calcite) was reported. However, little information on silica precipitation and its effect on concrete properties has been revealed. In this present study, the concrete specimens were incorporated with Bacillus subtilis silica adsorbed in their cell wall. Concrete specimens with five different concentration of Bacillus subtilis cell which are 104, 105, 106 and 107 cell/ml and control (without Bacillus subtilis) were cast. The experimental investigation aims to prove that the silica precipitated by this microorganism can enhance the concrete properties namely its compressive strength and resistance to carbonation. The microstructure of the concrete contained Bacillus subtilis was also examined. It appears that the inclusion of Bacillus subtilis into the concrete enhanced the compressive strength. The concentration of 106 cell/ml was found to be the optimum concentration to give most enhanced effect to the compressive strength. However the effect of including Bacillus subtilis to the resistance to carbonation of the concrete specimen is found to be insignificant.
Abstract. Bottom ash is a solid residue produced through combustion process in a coal-fired power plant. It has been catogarized as a waste and usually disposed in the utility disposed site. With higher demand on the power energy, more coal-power plant are constructed and abundance of bottom ash are produced. Recently, the utilization of bottom ash in the construction industry has gained the interest of researches. Since it has similiar particle size distribution as normal sand, many attempt has been made in studying it potential use in mortar and concrete. In complementary to that, this paper presents the effect of bottom ash on fresh and hardened properties of self-compacting concrete (SCC). Bottom ash is used as fine aggregate replacing sand with replacement ratio range from 0% to 30% by volume. The effects of bottom ash on the SCC were investigated by comparing the test result of SCC mixed bottom ash with control specimens (0% of bottom ash). The test result on fresh properties of the concrete mixture revealed that, as the replacement level of bottom ash increased, the slump flow, L-box passing ratio and segregation resistance ratio (SR) decreased. Nevertheless, the slump flow time (T 500 ) result increased with the increased of bottom ash content. The results show that the porosity and the irregular shape of the bottom ash particle has great influence on workability and viscosity of the fresh concete. The compressive strength and water absorption test are carried out on the sample at curing time of 7 and 28days. In terms of strength, the use of bottom ash in the production of SCC has increased the compressive strength of the concrete up to 15% replacement level. The increase in strength show the presence of the pozzolanic reactivity in a concrete with bottom ash particle. The water absorption rate was observed to be lower with a sample which having 10% and 15% replacement level.
Mechanical means of ventilation and air-conditioning system in Malaysian buildings are used continuously to provide and maintain the comfort of indoor environment to the occupants of the buildings. It was found that the system used led to higher rate of energy consumption. Hence, development of masonry units with high thermal insulation properties is a necessity. This paper represented the study on the thermal conductivity and the density of sand-cement blocks incorporated with different proportions of kenaf (Hibiscus cannabinus L.) fiber as additive. The amount of kenaf fiber inclusions were the main focus to observe the achievement of best results for both properties. It was found that kenaf fiber content had an advantage to reduce the self-weight of blocks whilst reducing the thermal conductivity property. Hence, it can be seen that there is a potential in developing masonry units for single wall components in Malaysian buildings with lightweight features and thermal insulator properties.
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