Optimum Mix Design for Internally Integrated Concrete with Crystallizing Protective Material

In this research, a silica-based crystallizing protective material was integrated into a fresh concrete mix to evaluate its efficacy in reducing water absorption while preserving the compressive strength level of the mixture. An optimum concrete mix design was determined, by producing several concrete mixes with different water-to-cement ratios (w/c) of 0.32, 0.37, 0.40, and 0.46, and treated with 2% and 4% of the crystallizing admixture. Water absorption and the mechanical properties of the treated and control mixes were measured, using the initial surface absorption test (ISAT) and the compressive strength and the flexural strength tests, respectively. Results showed that it is possible to obtain a water-resistant concrete without compromising its compressive strength if the right w/c ratio was used and the proper dosage of the crystallizing material was added. In addition, results revealed that treatment is beneficial only in the case of producing concrete with low w/c ratios of 0.32 and 0.37 and treated with crystallizing material. The compressive strength can increase up to 42% and with a significant drop in water absorption reaches 65%. Treated concrete was analyzed thoroughly under the scanning electron microscope (SEM) and X-ray diffraction (XRD) instrument to show the development of crystals with time and their interaction with the concrete mix.