Papers by Author: Sotiris Tsivilis

Abstract: In this paper the diffusion of chloride ions through limestone cement concrete is studied. The Portland limestone cements have many benefits and the new European Standard EN 197-1 identifies 4 types of Portland limestone cement containing 6-20% limestone (types II/A-L and II/A-LL) and 21-35% limestone (types II/B-L and II/B-LL), respectively. Portland limestone cements of different fineness and limestone content (0-35% w/w) have been produced by inter-grinding clinker, gypsum and limestone. Six concrete mixtures were prepared and the Nordtest Method (accelerated chloride penetration) was applied for the determination of penetration parameters for estimating the resistance against chloride penetration into hardened concrete. The diffusion equation of Fick’s second law was used for the determination of the effective chloride transport coefficient. It is concluded that Portland limestone cement concrete indicates competitive behavior with the Portland cement concrete. Limestone content up to 15% has a positive effect on the concrete resistance against chloride penetration.

Abstract: In this paper the effect of chlorides on the thaumasite form of sulfate attack in limestone cement concrete is studied. Concrete specimens made from ordinary Portland cement and two Portland limestone cements (limestone content 15% and 35% respectively) were prepared. After 28 days of curing the specimens were immersed in six solutions of various sulfate and chloride content and stored at 5oC. Visual assessment of the specimens, mass measurements and compressive strength tests took place for a period of 24 months. XRD method was used to identify thaumasite in the deteriorated parts of the specimens. All measurements showed that Portland cement concrete exhibits a lower degree of deterioration than Portland limestone cement concrete. Specimen disintegration was more severe, the higher the limestone contents of the cements and the higher the sulfate content of the corrosive storage solutions. Chlorides play an inhibitory role, delaying the deterioration of the concrete specimens. XRD analysis showed the presence of thaumasite at the deteriorated parts of the specimens after nine months of curing.

Abstract: In the present work the geopolymerisation of blast furnace slag (GGBS) under varying conditions is being investigated. The experimental comprises the following parts: i) dissolution of slag in alkaline media and the investigation of the effect of the alkali ion (K or Na) on the dissolution of Al+3 and Si4+, ii) synthesis of slag based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkaline ion on the development of the compressive strength and iii) characterization of geopolymers by means of XRD, FTIR and SEM/EDS measurements. As it is concluded, blast furnace slag geopolymers exhibit high compressive strength, with the maximum being 112.7±2 MPa. The Si/Al ratio of the starting material is found to affect strongly the development of the geopolymer compressive strength. The microstructure of slag–based geopolymers and the incorporation of Ca in the geopolymer matrix are also discussed.

Abstract: In the present work the geopolymerisation of metakaolin under varying conditions is investigated.The experimental part comprises the following parts: i) the synthesis of metakaolin based geopolymers and the investigation of the effect of the Si/Al ratio and the kind of alkali ion on the development of the compressive strength and ii) the characterization of the geopolymers by means of XRD, FTIR and SEM. As it is found the development of the compressive strength is strongly affected by the Si/Al ratio in the starting material and the kind of alkali metal, with the maximum being 70.1 MPa for a Si/Al ratio equal to 2.00. The Na- geopolymers show higher compressive strength compared to the NaK-geopolymers. Finally, low Si/Al ratios favour the formation of crystalline compounds (mainly zeolites), while Si/Al ratios higher than 1.5 lead to the formation of amorphous materials.