Effect of Cellulose Ether and Nanoclay on Rheology and Segregation Resistance of Cementitious Grouts for Post-Tensioning Applications

The growing use of post-tensioned (PT) concrete systems in large infrastructure projects demands a durable tendon protection system to achieve the long target service life. To protect the tendons embedded inside the PT ducts from premature corrosion, ducts should be filled with flowable and highly bleed-resistant cementitious grouts. This paper discusses the effect of cellulose ether and highly purified palygorskite clay (nanoclay) particles on the rheological behavior, bleeding or segregation performance, and robustness of the cementitious grouts used for PT applications. The grouts are formulated with portland cement, class F fly ash, polycarboxylate ether–based high-range water reducer, cellulose ether–based viscosity modifying agent (VMA), and nanoclay. All the ingredients were in powder form and preblended before the wet mixing. It was observed that the addition of cellulose ether or nanoclay could yield a very high bleed-resistant grout without compromising the flow characteristics. Although the grout with nanoclay exhibited a highly thixotropic nature compared to grouts with VMAs, the initial fluidity was lower than that of the grout with VMAs. From a desorptivity-based approach, an index that considers the induced pressure on the grout and duration of pressure application was proposed to distinguish the PT grouts with the desired bleed-resistance capability. From the comprehensive performance analysis, it can be concluded that the highly bleed-resistant grout with cellulose ether or nanoclay can be best utilized for the applications like grouting of PT tendons.