Investigation of microstructure-compressive strength relationship of cement mortars

A relationship between the microstructure formation and compressive strength of cement mortars has been established in the scope of this thesis. Microstructure properties such as; pore area ratio, total pore length (TL), total dendrite length (TDL) and average roundness (AR) of pore phases were determined by microstructural investigations. Also, hydrated part area, Ca(OH)2 phase area and unhydrated part area ratios were calculated based on image analysis methods. The influence of incorporation of chemical admixtures (retarders) at different dosages on the development of these phases has also been investigated. A decrease in the development of hydration products has been observed with the increasing dosages.A delay on the development rate of compressive strength by incorporation of chemical admixtures at early ages has been determined. The highest strength values were obtained for the cement mortars prepared by naphthalene sulphonate based chemical admixtures. The strength values of specimens prepared with overdosage were lower than those of control specimens. Six parameters (pore area ratio, total pore length, total dendrite length, average roundness, hydrated part area ratio and unhydrated part area ratio) were correlated to compressive strength values of different mixtures.Although this relationship is strong, multiple linear regression investigations indicate that determination of only two parameters (total dendrite length and hydrated part area ratio) is sufficient enough to represent the relationship of microstructural formation-compressive strength confidently. This analysis indicates that the connected channel system of pore phase is more effective on strength than the amount of pore phase.