Optimizing grout formulations for post-tensioning using pozzolanic and filler blends

The use of post-tensioning (PT) technology has grown rapidly due to the increasing demand for longer spans and reduced section depths in concrete structures. However, conventional grout used in bonded PT systems often suffers from bleeding and segregation, leading to void formation, tendon corrosion, and reduced durability. To overcome these issues, high-performance grout (HPG) mixes are typically produced using supplementary cementitious materials (SCMs) such as silica fume and fly ash. Although effective, these materials are expensive and not always readily available. This study investigates the feasibility of using limestone powder as a cost-effective and locally available alternative to traditional SCMs. Thirteen grout mixes were developed with varying water-to-cementitious material ratios (0.27-0.45) and partial replacements of cement by limestone powder (25% and 35%), fly ash (25% and 35%), and silica fume (2-10%).Experimental results demonstrated that increasing limestone powder content reduced bleeding from 1.4% to 0.5% due to its filler effect, but also increased efflux time beyond 50 s and reduced compressive strength from 35 MPa to 24 MPa. In contrast, silica fume-based mixes exhibited superior performance, achieving compressive strengths of 40-55 MPa, bleeding rates below 0.2%, and efflux times of 23-26 s, fully complying with ACI/PTI HPG standards. Fly ash improved workability and long-term strength but did not fully control bleeding. Overall, silica fume provided the best balance of strength, flowability, and durability, while limestone powder served as a low-cost, non-reactive filler capable of moderately enhancing bleeding resistance. The findings indicate that limestone powder can be utilized as a partial substitute for costly SCMs in resource-limited regions, contributing to more sustainable and economical PT grout formulations.