Indian Journal of Engineering & Materials Sciences Vol. 11, February 2004, pp. 63-67 Taguchi approach for investigation of the setting times on cement-based grouts Özcan Tan* & A Sahin Zaimoglu Ataturk University, Engineering Faculty, Civil Engineering Department, 25240 Erzurum,Turkey Received 6 August 2003; accepted 30 December 2003 Investigations on the effect of the bentonite, fly ash and silica fume on the initial and final setting time of cement-based grouts are reported here. Three additives (bentonite, fly ash and silica fume) were used in the grout mixes to improve the setting time of the grouts. Taguchi method was employed for the experiments and standard L16 orthogonal array with 3 pa- rameters and 4 levels were chosen. Experimental results show that the most efficient materials for the initial and final set- ting time are silica fume and bentonite, respectively. The initial and final setting times have been found to decrease rapidly with the increase in silica fume and bentonite ratio, while they rapidly increase with the increase of fly ash ratio. The Ta- guchi method has been found to be suitable for such studies. Cement-based grouts have been used in geotechnical engineering to solve foundation problems related to bearing capacity enhancement, reduction in the per- meability and settlements. Grout design involves the study of the behavior of a suspension in the fresh and hardened state. The requirements of a grout in fresh state are: high penetrability, stability of the suspen- sion, and limited or no bleeding 1 . One of the most important properties of a fresh grout is its initial and final setting times. The setting characteristics of ce- ment grouts are influenced by various factors, such as cement type, cement content, water content of fresh grout and properties of additive materials. The initial setting time represents the time at which fresh grout can no longer be properly handled or injected; and the final setting time approximates the time at which hardening and development of strength commence. The information on time required for grout to achieve the initial and final set is of great importance in the field 2 . In the field, initial and final setting times pro- vide a guide of available time for injection of a given batch. Also, very short and controllable set time may be required for injection into a soil layer with a water flow to avoid washing of the grout before it hardens 3 . The performance of grouts can be extended by the use of some admixtures. Bentonite (B), fly ash (FA) and silica fume (SF) are widely used in grouting applica- tions since they reduce the cost of the cement and re- duce the environmental problems. Bentonite is typical clay generated from the alteration of volcanic ash. Bentonite shows strong colloidal properties and its volume increases several times when coming into contact with water creating a gelatinous and viscous fluid. The special properties of Bentonite such as hy- dration, swelling, water absorption, viscosity make it a valuable material for grout applications. FA is a by- product of the combustion of pulverized coal in ther- mal power generation. FA contains mainly silica and alumina. Also, the fineness of FA is similar to ordi- nary Portland cement. SF is an extremely fine powder obtained as a by-product in the manufacture of silicon metal or silicon alloys. Silicon metal and silicon al- loys are produced in electric arc furnaces. The silica content in this material varies from 85% to 98%. Be- cause of extreme fineness and silicon content, SF is a highly effective pozzolan. The properties of cement grout are influenced by various properties of additive materials, such as physical properties, particle shape and size, specific gravity, uniformity, moisture con- tent, carbon content, pozzolanic activity, content of SiO 2 +Al 2 O 3 +Fe 2 O 3 and loss on ignition. When the additives are used together in a cement based grout mix, they should be properly proportioned and mixed to control setting time, bleeding, viscosity, strength, etc. The effects of admixtures in the cement grouts have been reported earlier 4-7 . The aim of the present work is to investigate the ef- fects of the three admixtures (FA, SF and B) on the setting times of the grout mixes. More detailed infor- mation about this study can be found in Zaimoglu 8 . The experimental work was so designed that the ex- periments gave the optimum working conditions of —————— *Author for correspondence (e-mail: oztan@atauni.edu.tr )