Effect of mineral admixture types on the grout strength of fully-grouted rockbolts

This paper represent the results of an experimental study handled with developed grouting materials for fully-cement-grouted ribbed rockbolts. These experimental studies cover the effects of some mineral admixtures (silica fume, blast furnace slag, fly ash etc.) on the bond characteristics between grout and rockbolts. The effect of mineral admixtures on the grout strength of fully-grouted rockbolts and block punch index (BPI) and compressive strength (CS) of the grout on the load bearing capacity (LBC) were investigated. Totally 150 rockbolt pull-out tests were performed using ten different grouts in order to investigate and improve the LBC of grouted rockbolts for five different curing times (1, 3, 7, 28 and 90 days). All grout types were prepared same ratios, and silica sand was used as fine aggregate. Grout mixtures that 15% of mineral admixtures replaced with cement by weight were prepared. The results showed that grouts produced with silica fume (SF) and metakaolin (MK) in all mixtures were yielded the highest CS and bond strength at all ages. The all strength tests of fly ash (FA) grout exhibited low values till 28 days of curing time in accordance with reference grout, but a sharp increase was observed after this period. Grouts with perlite (PRL) and blast furnace slag (BFS) showed the similar strength values according to reference grout. In conclusion, mineral admixtures can be used for high-strength and low cost grout in tunneling applications. In addition, the use of waste materials can contribute to the resolution of environmental problems.