Investigation of the Effect of Nano SiO2 on Porosity

Date of Award


Degree Name

M.S. in Civil Engineering


Department of Civil & Environmental Engineering & Engineering Mechanics


Advisor: Joseph Saliba


Concrete is naturally porous and allows water to penetrate its surfaces. This water penetration can easily deteriorate the concrete and cause chemical attacks, weakening its durability and strength. Thus, improving porosity will improve its quality, durability, and life span. This study investigates ways to enhance concrete porosity without harming compressive and flexural strengths. This study focuses on adding nano SiO2 (0%, 1%, 2%, 4% and 6%) while keeping constant the amount of fly ash (2%) and water cement ratio (0.41). The benchmark used was simply plain concrete without fly ash or nano SiO2. This was accomplished by testing a total of 36 cylinders after allowing the concrete to cure for 28 days. In this study, results show that porosity decreases with the addition of nano SiO2 until it reaches (1%) optimum value, which is 5.9% lower than the plain concrete (without additive). However, the porosity altered after the 1% optimum value; porosity increased with the addition of 4% and 6% nano SiO2, but it was still lower than the concrete with fly ash and the plain concrete (without nano SiO2 or fly ash). For compressive strength, the results show that among four different nano SiO2 percentages, the addition of 2% nano SiO2 with fixed 2% fly ash has a higher compressive strength, which is 17.3% greater than the strength of the reference 0% nano SiO2. However, the increase in compressive strength was altered after the addition of 2% nano SiO2. The addition of 4% and 6 % of nano SiO2 decreased the compressive strength and lowered the workability of the mix. Once the optimum percentage of SiO2 was found (1%) and making sure that no deterioration of compressive strength occurred, the flexural strength (rupture strength) was checked using a three-point method. Nine beams are used for the flexural test for 28 days; three of the nine beams use concrete with the optimum value from the porosity test. In the flexural test, the results show that the addition of 1% nano SiO2 combined with 2% fly ash increased the flexural strength to a higher value than both concrete containing 2% fly ash and the plain concrete (without nano SiO2 or fly ash).


Civil Engineering, Effect, Nano Silica, Nano SiO2, Concrete strength, concrete porosity, Flexural strength

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