Strengthening of Unreinforced Masonry Walls using ECC Shotcrete

Abstract

This doctoral study investigated the use of Engineered Cementitious Composite (ECC) shotcrete, a sprayable fibre reinforced mortar that exhibits a strain-hardening characteristic, for the seismic strengthening of unreinforced masonry structures. Additionally, the feasibility of utilising ECC shotcrete as a chloride resistant cover concrete to improve the service life of reinforced concrete structures was examined. A series of laboratory tests quantified the ECC shotcrete tensile characteristic properties using a new technique, with the results adopted for the structural analysis and design of ECC strengthened walls. Subsequent laboratory testing defined the chloride diffusion coefficients of multiple ECC mix designs, indicating that increased fly ash content significantly improved the chloride resistance. Life cycle modelling showed that assuming an uncracked state throughout the structure service life, replacement of the investigated 40 MPa concrete with the best performing ECC shotcrete mix for steel reinforcement cover could provide a service life extension of up to 42 years. Testing of 25 clay brick wallettes subjected to in-plane loading showed that ECC application increased wall capacity by up to 5.1 times their as-built state. Masonry wall thickness and ECC overlay thickness were the key parameters affecting strengthened clay brick wall performance. Testing of 26 concrete block masonry wallettes determined the effect of ECC applicator skill and application method on wall performance, with strength reduction factors introduced to account for this effect. Using the experimental results, an in-plane masonry wall strengthening design procedure was proposed. Testing of five ECC strengthened clay brick masonry walls subjected to out-of-plane loading showed a 12.7 times strength increase when ECC overlay was applied to the wall tensile surface and a strength increase of 3.4 times when ECC overlay and near surface mounted steel reinforcement was applied to the wall compression surface. Strengthened wall capacity was predicted using existing concrete flexural design methodologies, and design procedures for out-of-plane strengthening of clay brick masonry walls were proposed. An ECC shotcrete based seismic strengthening design was developed for a 1917 two-storey in-service unreinforced masonry building utilising the material properties and design methodologies defined in this doctoral study. No significant application issues were identified during the implementation process, and the current results support the use of ECC as a seismic strengthening system for masonry buildings.