การประยุกต์ใช้เอฟจีดียิปซั่มเป็นสารผสมเพิ่ม เพื่อช่วยการขยายตัวของซีเมนต์เกราท์

Abstract

Possible applications of using flue-gas desulfurization gypsum (FGD Gypsum) as an admixture for cement grout expansion were studied in this research especially for ground anchor usage. Laboratory and field tests were operated. In laboratory test, several mixtures were done to determine the influence of amount of gypsum to compressive strength and grout expansion of hardening cement. The results showed that the increasing of FGD Gypsum can increase the expansion rate, but the compressive strength was dropped. If the gypsum mixture with less than 6% mixing with fly ash and lime, the expansion property could increase while the compressive strength was still unchanged. The best ratio is 90:7:3 for cement :fly ash :: lime respectively. For the admixture of 4% gypsum at the age of 28 days, the compressive strength increased at 15% and expansion rate increased at 6%. Tensile strength was tested in laboratory showing the important of grout mixtures. The mixture of cement, fly ash, and lime adding with gypsum could increase expansion rate at 3.4% and tensile strength increased at 26% comparing to 14% of the same grout admixture with limited expansion. The grout mixture with 2% and 4% gypsum (with expansion rate of 2.7% and 3.4%) increased the tensile strength from 15% to 25% and 14% to 26% respectively.

In field test, pull out test was used for three sets: grout mixture for ground anchor with gypsum, fly ash, lime comparing to ground anchor with only cement, and general usage for cement and admixture for expansion. The results showed that mixture of cement : fly ash : lime with increasing of 2% gypsum increased the ratio of shear strength to compressive strength to 23%. For the current usage of expansion admixture caused the ratio of shear strength to compressive strength to 20% while the only cement admixture caused the ratio of shear strength to compressive strength to 16%. The result also showed that the mixture with the highest ratio of shear strength to pull out strength is the same as the mixture with the highest ratio of shear strength to compressive strength. The failure of the ground anchor was the failure of bond at the surface between steel and cement grout. The comparison of laboratory and field tests showed that the less expansion rate 2% for limited expansion and 6% for unlimited expansion. It could be seen that the limited expansion of soil around ground anchor causing the ratio of shear strength to compressive strength increased; however, in laboratory test the ratio was slightly high comparing to the field test.