Improving Concrete Properties with Rice Straw Ash, 2017


Project Leader

Feraidon Ataie, program coordinator, Concrete Industry Management Program, CSU Chico

This program previously investigated the use of rice straw fibers as an internal curing agent for concrete. In a new study, researchers at California State University, Chico, investigated the use of rice straw ash on alkali-activated slag cement. According to the U.S. Environmental Protection Agency, use of slag in concrete will help reduce greenhouse gases.

This is a two-year research project. In 2017, rice straw was immersed in water for 24 hours and then dried and burned at 1,112 degrees Fahrenheit for one hour. The ash was then ground to produce a powder.

The slag was mixed with sand and a 4-mole sodium hydroxide solution to make mortar cube samples containing 5%, 10%, or 20% rice straw ash. Another set of samples was made by presoaking rice straw ash in sodium hydroxide solution for 24 hours. Also, two sets of samples were made by adding 25% and 12.5% sodium silicate to the mix instead of rice straw ash. Moist samples were then cured at 73 degrees Fahrenheit. Compressive strength tests were measured at three, seven, and 28 days.

The samples were compared with those that did not include rice straw ash in the mix. Results indicate that adding rice straw ash in alkali-activated slag increases compressive strength. Furthermore, presoaking rice straw ash before adding it to the mix increased the compressive strength dramatically. Samples with a compressive strength of of more than 6,000 pounds per square inch were achieved in seven days, a remarkable result.

Research in 2018 will examine performance of rice straw ash in alkali-activated slag systems at a higher curing temperature of 104 degrees Fahrenheit. Rice straw ash will be added at 5%, 10%, and 15%, with and without presoaking. Compressive tests will be measured at three, seven, and 28 days. Moreover, the intent is to test sodium hydroxide solution at a lower concentration (2-mole) and compare results to that of 4-mole solution.