Effect of mineral admixture types on the grout strength of fully-grouted rockbolts Ahmet Teymen Department of Mining Engineering, Engineering Faculty, Ömer Halisdemir University, 51240 Nigde, Turkey highlights  Bolt bond strengths and bearing capacities of grouted rockbolts were investigated.  Mineral admixtures increased the pull-out capacities of rockbolts.  Mineral admixtures can be used in grout to achieve higher resistance.  The predictive models were developed for estimating bond strength of rockbolts. article info Article history: Received 12 January 2017 Received in revised form 28 March 2017 Accepted 7 April 2017 Keywords: Rockbolt Grout Admixture Block punch index abstract 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 val- ues 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 resolu- tion of environmental problems. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction The rockbolts support system has often been used in the long- term stabilization of underground excavations in rock masses. Rock bolt systems can be divided into three groups, which are mechanically anchored, friction anchored and fully-grouted rock- bolts (resin and cement grouted rockbolts). Developments of set- ting techniques and equipment, not having a disadvantage of decreasing at intersectional area of cavern, having a reinforcement effect in addition to supporting effect made rockbolts unrivalled in tunneling and slope stability. The cement-grouted rockbolt is a fully-grouted rockbolt with- out mechanical anchoring. It generally consisting of a ribbed bolt inserted in a drillhole and bonded to the drillhole periphery over its embedded length. Bonding medium of rockbolts is cement mor- tar. The parameters controlling the LBC of cement-grouted rock- bolts are shape of bolt, diameter of bolt, length of bolt, the rock and the grout strength. The major mechanism that determines the bond strength of fully-grouted rockbolts is friction. Friction depends on the shear strength at the rock-grout or bolt-grout interface. Fully grouted untensioned rockbolts have been used for many years in civil and mining engineering projects. However, only a few works have been reported on strengthening of grouting materials using mineral and chemical admixtures. http://dx.doi.org/10.1016/j.conbuildmat.2017.04.046 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved. E-mail address: ateymen@ohu.edu.tr Construction and Building Materials 145 (2017) 376–382 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat