Factors affecting the performance characteristics of cementitious grouts for post-tensioning applications

In grouted post-tensioned (PT) systems, cementitious grouts are supposed to completely fill the interstitial spaces between the strands and act as the 'last line defence system' against corrosion. However, use of poor quality grout materials and grouting practices result in voided grout systems, ultimately leading to premature failure of tendons in many bridges around the world. To ensure an intact system, the grout must have excellent fresh properties, in particular the flow properties. Such high-performance grouts are not available in many developing countries, where grouting for post-tensioned structures is still a nascent technology. In this research, a two-stage test program was carried out to evaluate the fresh and hardened properties of seven commercial grouts, which includes three Pre-Packaged Grout mixes (PPG); three Site-Batched Grout mixes (SBG) and one standard Ordinary Portland Cement grout mix (PCG). Further, one PPG mix and SBG mix were chosen and their properties were evaluated for three levels of mixing speed and two ambient temperature conditions. Fresh properties such as wet density, efflux time and its retention, standard bleed, wick-induced bleed and pressure bleed, as well as set/hardened properties such as setting time, compressive strength and volume change were evaluated. Three batches of grout were tested for each grout material, to ensure reliability of results. The influence of binder fineness on the performance of grouts was also evaluated. The study serves as a strong evidence in substantiating that the most commonly used grout materials for PT system in developing countries, fail to meet the standard requirements and even the manufacturer's own specifications. It is also found that the performance of the grout is influenced by mixing speed, ambient temperature, and fineness. The study emphasises that the evaluation of the grout behaviour under simulated field conditions is essential to ensure void free and durable PT systems. (C) 2018 Elsevier Ltd. All rights reserved.