PENETRATION OF CEMENT PASTE INTO LIGHTWEIGHT AGGREGATE

Mix proportioning of lightweight concrete is generally less accurate than that of normal weight concrete. From time to time it has been speculated whether a part of the cement paste from the fresh mix also penetrates into the aggregate. This paper presents an experimental investigation on penetration of cement paste into the lightweight aggregate. During mixing of lightweight aggregate concrete the cement paste will penetrate most of the open pores in a surface layer of the aggregate. However, a deeper penetration of silica fume particles from the cement paste was not observed. The amount of paste penetration depends on the microstructure of the surface layer of the aggregate, the particle size distribution of the cement and silica fume, and the viscosity of the paste. Since the microstructure of the surface layer may vary from one type of aggregate to another and also within the same aggregate, it may be difficult to quantify the amount of cement paste penetrating into the aggregate. In addition to water absorption, penetration of cement paste further adds up to the unaccuracy in the mix design of lightweight aggregate concrete.