Mariah Martinez

Concrete is by far the most widely used building material in the world. However, concrete’s strength and durability is accompanied by a weakness, cracking.  One form of cracking can occur when water evaporates from concrete causing shrinkage due to the action of the surface tension of water within the minute pores of concrete.  Although a number of effective shrinkage reducing admixtures are already commercially available, when taking into consideration environmental impact, strength development, and overall shrinkage protection, there is still much room for improvement.

Our group has recently demonstrated that computer aided molecular design (CAMD) using an inverse quantitative structure activity relationship (I-QSAR) is an effective tool for identifying compounds that reduce the surface tension of water [1, 2].  Not all good surface tension reducers, however, make good shrinkage reducing admixtures (SRAs) since many have unwanted side effects.  After identifying a compound with great potential as an SRA, it was found that is also interferes with the setting behavior of concrete. When test mortar bars were soaked in a bath containing a small dose of the compound for seven days, the post cure drying shrinkage of the mortar was reduced by more than twice that of a commercial admixture administered in the same manner. This leads to the question: if the concrete would set properly, could this admixture reduce shrinkage effectively when directly applied to the mix water. When soaked in the new admixture for seven days, a precipitate formed on the surface of the mortar bar, leading to the question of whether or not the precipitate or the compound is responsible for reducing the subsequent drying shrinkage. In response to this question, I am attempting to measure the rate of diffusion of the agent into the mortar bar using various measures such as electrical conductivity and ion chromatography.  Also, microstructural analysis of the seven-day cured (soaked) mortar samples carried out using X-ray diffraction and scanning electron microscopy (SEM) is being done to identify the precipitate and to characterize any microstructural changes that might be occurring. Results from these experiments should elucidate the effect of both the precipitate and the agent.  In combination with molecular modeling studies, our team hopes to identify ways to modify such compounds to retain desired properties will mitigating side effects.

[1] H. M. Kayello, N. K. R. Tadisina, N. Shlonimskaya, J. J. Biernacki and D. P. Visoc Jr., An Application of Computer-Aided Molecular Design (CAMD) Using the Signature Molecular Descriptor – Part 1. Identification of Surface Tension Reducing Agents and the Search for Shrinkage Reducing Admixtures, J. Am. Ceram. Soc., 97(2), 365-377 (2014).

[2] N. Shlonimskaya, J. J. Biernacki, H. M. Kayello and D. P. Visoc Jr., An Application of Computer-Aided Molecular Design (CAMD) Using the Signature Molecular Descriptor – Part 2. Evaluating Newly Identified Surface Tension Reducing Substances for Potential Use as Shrinkage Reducing Admixtures, J. Am. Ceram. Soc., 97(2), 378-385 (2014).