Development of a reconstituted brown coal material using cement as a binder

Abstract

Like any other coal, the highly heterogeneous nature of brown coal can sometimes make it difficult to interpret the results of laboratory experiments. More homogeneous samples with properties reproducible in the laboratory would provide significant advantage, especially in understanding the effects of various factors in the properties of coal. An attempt was made to develop reconstituted coal (RC) samples in the laboratory through an extensive material development and laboratory testing programme. The latter consisted of mainly uniaxial compression tests. The main objective in developing the RC material is to use it in future research on CO2 sequestration in unmineable coal seams. A highly homogeneous coal sample would make it much easier to identify, for example, the effect of CO2 sorption on the mechanical, flow and transport properties of coal. Uniaxial compression tests were conducted on some brown coal samples to determine the approximate mechanical properties. The results revealed an average uniaxial compressive strength of 1.46 MPa, an average elastic modulus of 77.43 MPa and a Poisson’s ratio of 0.16. The measured properties were used as a reference for the development of RC samples. An extensive laboratory experimental programme was conducted to develop RC samples with the desirable mechanical properties. Portland cement was used as the cementing agent for the RC. Different variables such as percentage of cement, water content, compaction load and curing time were taken into account when developing RC samples. Uniaxial compression tests were carried out to ensure that the RC samples were reasonably homogeneous and the properties were similar to those of natural coal. Percentages of cement by weight of coal such as 4, 6 and 8% were attempted and a 4% cement mix with 50% water was considered most suitable for the RC samples. Average compressive strength of 0.8 MPa (28-day strength) and an average elastic modulus of 34 MPa were achieved for the RC samples. Further efforts at improvement would involve better matching of the uniaxial compressive strength and elastic modulus of RC samples with the natural coal samples.