New On-Site Wet Milling Technology for the Preparation of Ultrafine Cement-Based Grouts

Abstract

The use of ultrafine cement-based grout has been gaining importance for rock and soil grouting over the last few years. One of the more dramatic technical innovations in the grouting industry that has been sought is the ability to mill, on-site, a fine or ultrafine cement-based grout using regular cement, and locally available additives (fly-ash, pumice, slag, bentonite, clay, tailings, catalysts, sand). This paper presents the results of extensive research and testing program executed during the development of a mobile Particle Size Reduction Mill (PASREM). The search for an inexpensive and effective milling machine for on-site production of ultrafine cement-based suspension grout has been ongoing since the early 1990's. The application of on-site milling would solve the problems associated with the use of classic pre-prepared ultrafine cement. This includes the agglomeration of particles that often results in a grout with a higher average particle size than desired, reducing penetrability of the grout, and the high cost of ultrafine cement. On-site milling would also allow for the use of many locally available products and additives that could enhance the final grout and reduce the cost of producing the grout. PASREM is a mobile milling machine used to produce ultra fine cements from readily available portland cements and additives. This process is preferably done by injecting a balanced cement-based suspension grout through the PASREM, immediately prior to grouting. This is further referred to as the wet milling process. The PASREM process can also be used to mill the aforementioned dry powders to microfine size, to produce a classic (bagged) microfine cement. The History of Wet Milling The wet milling process is not a new concept. In 1992, Rodeo announced the first wet mill production process (Bosco et al., 1992) referred to as the Cemill process. This process did not break through a number of problems: the coagulation of particles, rapid gelation of the grout, a sensitive and complex operation as well as some practical factors. In 1993 Sandia National Laboratories also undertook the development of a wet milling process (Ahrens, 1993). This process was slow and cement particles began to coagulate and flocculate in the machine and the end product did not have the desired 1 President, ECO Grouting Specialists Ltd., 293199 8 Line, Grand Valley, ON, L0N 1G0; Tel. (519) 928-5949; anaudts@ecogrout.com 2 Senior Engineer, ECO Grouting Specialists Ltd., elandry@ecogrout.com