Influence of Raw Kaolin Clay and Its Dehydroxylated Form on The Properties and Performance of Portland Cement Mortar

Abstract

Kaolin, also known as China clay, is one of the materials that can be used as partial replacement for Portland cement but most of the research has been focused on its dehydroxylated form (metakaolin). The lack of interest in raw kaolin clay as a cement replacement material is partly due to its negative impact on strength and the traditional perception that raw clay is detrimental to concrete. However, the use of raw kaolin clay as cement replacement may offer other benefits, such as energy saving and the potential to produce durable cement-based material at low cost. Therefore, this paper presents findings on the influence of raw kaolin clay on the properties and durability performance of Portland cement mortar in comparison with metakaolin, when used as partial substitute. The results show that the use of raw kaolin clay as a partial substitute for Portland cement improved all aspects of the durability properties investigated, which became more apparent with age. Despite having the lowest compressive strength, the raw kaolin clay mix displayed a lower porosity, better resistance to water absorption and finer pores than the control. In contrast to the raw kaolin clay, the metakaolin significantly enhanced both strength and durability. The results also reveal that at a given superplasticizer dosage and replacement level, the kaolin and metakaolin mixes exhibited the same consistency in the fresh state and a similar range of pore size distribution and total intrusion volume at 28 days. The findings further demonstrate that raw kaolin clay can be used as Portland cement replacement material to produce durable mortar and concrete, particularly for applications that do not require high strength.