Durability and Microstructure of Pore Reduced Cements (PRC)
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ABSTRACT The pore structure characteristics of cementitious materials play an important role in defining their mechanical and durability performance. The mechanical properties of pore reduced cements (PRC) have already been reported [5] as a function of the product density. This paper reports recent data on the durability of PRC and attempts to relate the pore properties of the material to its resistance against deterioration in aggressive environments.
INTRODUCTION Research into high performance cements is becoming increasingly important. This is partly due to a recognition that essential maintenance of structures made using traditional building materials and methods can be very expensive and also that traditional unreinforced cements and concretes have relatively poor flexural strengths. The relationship between the strength of a material and its porosity has been known for some time. MDF (macro-defect free) and DSP (densified system of homogeneously packed small particles) cements have been developed based on this knowledge and have much improved mechanical performances compared with normal cements. This has been achieved by minimising initial porosities using fillers with further porosity reductions arising due to chemical interactions at the filler-cement interface [1-4]. Reduction of volume porosity not only increases mechanical performance of a Portland cement paste but it also tends to change the nature of the pores and consequently paste durability. Essentially two types of pores exist. At high levels of porosity, interconnected pores will predominate under normal conditions. These have a significant influence on matrix durability, providing tortuous channels through which material transport can occur. Moisture movement and action of chemical species from the environment (e.g. sulfate, chloride, carbon dioxide) can lead to chemical degradation from within the matrix as well as on the external faces of the product. This effect is self-accelerating because degradation usually leads to increased porosity and increased intrusion. At lower volume porosities, the emphasis shifts towards isolated pores which are not connected to the outer boundaries of the product. These are therefore sealed from intrusion and leaching. Thus, the strength and durability performances of cementitious systems can be improved by reduction of porosity. It is however, the practical achievment of low porosity which has limited the commercial exploitation of high performance cements. While high densities and high strengths have been observed in MDF and DSP products, post-manufacture instability has also been observed due to the nature of the interactions between moisture, the cement and the filler materials. This paper is concerned with the porosity and durability characteristics of pore reduced cements (PRC) where porosity reductions are achieved using mechanical methods as an alternative approach [5,6].
237 Mat. Res. Soc. Symp. Proc. Vol. 370 0 1995 Materials Research Society
Pore reduced cements (PRC) [5.6] Pore reduced cements (P
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