G Alipour - Construction Materials Institute, School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran.
R Rashetnia - Construction Materials Institute, School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran.
A Dousti - Construction Materials Institute, School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran.
M Shekarchi - Construction Materials Institute, School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran.

Using of concrete as a structural material has been increased in recent years. It has been found that some concrete structures, even which constructed high performance concrete, start to deteriorate long before reaching their designed service life. That made using of them unsafe, showed that durability modification in concrete must be considered in construction and especially on repair of damaged structures.The durability of a concrete repair is dependent of many factors. Sulfate attack is one of the most aggressive environmental deteriorations that affect the long-term durability of concrete structures. The sulfate attack of concrete leads to expansion, cracking, and deterioration of many civil engineering structures exposed to sulfate environment such as piers, bridges, foundations, concrete pipes, etc. The sulfate ions in solution, which come from the soil, ground water, and seawater, are found in combination with other ions such as sodium, potassium, magnesium and calcium ions. Pozzolanic materials have an important role in the long term durability of mixtures exposed in sulfate environments. Their effect is thought to be explained by two primary mechanisms: the ‘‘dilution effect’’ (decrease of the C3A content of the binder when they replace a portion of Portland cement) and the ‘‘pozzolanic effect’’ (formation of secondary CSH). In this study, we are going to investigate the effect of several types of pozzolanic materials on cement paste expansion according to ASTM 1012 ‘‘Standard Test Method for Length Change of Hydraulic Cement Mortars Exposed to a Sulfate Solution’’.