The effect of effective microorganism solution as self-curing agent on properties of concrete

Abstract

The curing process ensures progress of hydration reactions which cause filling and discontinuity of capillary voids by hydrated compounds in newly placed concrete. In real practice, proper curing is a challenging task to achieve in structural elements such as inclined structures, high-rise buildings or structure with the thickness of concrete is large. Improper curing leads towards the poor quality of concrete. The objective and scope of the research is on examining the potential of Effective Microorganism (EM) solution as a self-curing agent to achieve the same or comparable properties of self-curing concrete (SCC) in air curing and normal concrete in water curing. The EM is eco-friendly bacterial solution used in agriculture. In methodology, three grades of concrete mixture were produced i.e. grade 30, grade 35 and grade 40 to analyse water loss from concrete and the effect of improper curing on concrete strength. The initial properties of tap water, EM solution and EM-water solution were investigated and identified. The optimisation of SCC with EM was based on the hardened properties of concrete. Six concrete mixtures were produced; one was normal concrete grade 30 (control) and other five mixtures were SCC in which the mixing water was replaced with EM by 5% to 25%. In order to determine the mechanism and internal composition of concrete in both curing regimes, microstructure analysis have been carried out. Results and discussion revealed that maximum water loss of 2% was recorded for grade 30. At the age of 28 days, the concrete sample in air curing experienced 23% less strength compared to samples in water curing. EM has low surface tension which makes it reliable for a self-curing agent. Thermal gravimetric analysis (TGA) results also showed that the EM evaporates at higher temperature than mixing water. The workability increased with increase of replacing percentage of water with EM. The slump testing was found in the range of 70–220 mm. The results also showed that the SCC with 10% of EM gave higher results of compressive strength of 53 MPa at 28 days in water curing. In air curing, SCC with 10% EM gained strength of 42 MPa, its strength was close to the strength of control concrete (43 MPa) in water curing. The water absorption and void of concrete were reduced with 10% of EM in SCC. Internal relative humidity (IRH) of SCC was found between 85-90% at 28 days with 10% EM, which is a favourable condition for complete hydration process compared to control concrete that ranges between 74-76% in air curing regime. It was noticed that the inclusion of 10% EM reduced temperature of SCC by 1-2oC. The 10% EM also showed 43% and 45% reduction in shrinkage and expansion, respectively in SCC as compared with control concrete. Result of the Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX) showed that concrete with 10% EM had a compact structure with fewer voids. TGA results revealed that 10% SCC gained 19% and 11% more C-S-H gel than control concrete in air curing and water curing, respectively. All the results showed that 10% of EM is the optimum value to get the desirable properties of SCC. Based on the findings, it is concluded that EM can be used in normal strength concrete to encounter improper curing as an efficient self-curing agent. The use of EM would not only contribute to the development of environmentally friendly materials, but also to the reduction of the emission of CO2 and the depletion of the earth's natural resources. The novelty of this research is the EM solution used as a self-curing agent. The contribution in the field of self-curing concrete is that it helps concrete to achieve the desired properties by changing the physical characteristics of mixing water.