Title: Influence of thixotropy on performance of grouts placed using vacuum injection techniques

Author(s): Joseph J. Assaad, Yehia Daou, and Jacques Harb

Publication: Materials Journal

Volume: 112

Issue: 2

Appears on pages(s): 189-198

Keywords: cohesiveness; fluidity; injection grouts; thixotropy; vacuum grouting.

DOI: 10.14359/51686914

Date: 3/1/2015

Abstract:
The injection of cementitious grouts by vacuum techniques is increasingly used in repair and new construction of posttensioning members. A research program was undertaken to assess the effect of thixotropy on water retention and behavior of grouts placed using such techniques. Tests were conducted using specimens sampled right after mixing as well as after being subjected to vacuum to extract part of the free mixing water. Test results have shown that the partial or complete extraction of free mixing water due to vacuuming decreases flowability (flowtime and mini-slump cone) and increases thixotropy of grouts, mostly due to increased cohesiveness and internal friction within the solid particles. Good correlations were established between extracted water and variations in thixotropy, air entrainment, wick-induced bleeding, unit weight, setting time, and compressive strength. Mixtures exhibiting more than 35% normalized extracted water are not suitable for grouting by vacuum techniques due to increased cohesiveness that hinders proper penetrability. A set of regression models was proposed to simplify product development and predict grout properties either in the fresh or hardened states.