Fresh and hardened properties of self-compacting concrete containing recycled fine clay brick aggregates

Hongzhi Zhang,Branko Šavija,Jiajie Wu,Huaqiang Yuan,Zhi Ge,Chen Fang,Erik Schlangen

doi:10.1617/s11527-021-01751-5

Abstract

Clay brick is one of the major components of demolition waste, which is generally landfilled. Effective and new uses of recycled clay brick may provide sustainability benefits in terms of landfill reduction. Therefore, this research aims at applying Recycled fine clay brick aggregates (RFCBA) with sizes from 0.075 mm–4.75 mm to prepare Self-compacting concrete (SCC). The effects of RFCBA on fresh and hardened properties of SCC were investigated. Saturated surface dry RFCBA was used to replace Natural fine aggregate (NFA) with the percentage of 25%, 50%, 75% and 100%, respectively, in making the SCC mixes. Although experimental results showed that the flowability, passing ability, and segregation resistance of SCC containing RFCBA (RFCBA-SCC) decreased with the increasing RFCBA content, these properties still satisfy the criteria of SCC. The compressive strength, splitting strength, flexural strength, and elastic modulus of the RFCBA-SCC mixes decreased with an increase of RFCBA content. Due to their porous nature, recycled fine clay brick aggregates may also be a source of additional water for internal curing. The internal curing effect was confirmed by the mercury intrusion porosimetry, X-ray diffraction, and thermogravimetric analysis measurements. Moreover, a significant autogenous shrinkage reduction of SCC is achieved by using the RFCBA due to the release of additional water pre-stored in the RFCBA. Therefore, it can be concluded that the addition of RFCBA to SCC mixtures can provide additional practical benefits in the hardened state.

Highlights

Due to its unique characteristics, e.g., high flowability, passing ability, and resistance to segregation, the use of Self-compacting concrete (SCC) has gained wide acceptance in recent years
The difference between slump flow and J-ring spread diameter is smaller than 25 mm, which means its passing ablitiy belongs to the PA2 as specified by the Chinese technical specification (Technical Specification for Application of Selfcompacting Concrete, JGJ/T283-2012) [42]
The blocking ratio decreases from 0.82 to 0.73, with replacement level of Natural fine aggregate (NFA) increasing from 0 to 100%. This can be caused by stronger cohesion between cement paste and Recycled fine clay brick aggregates (RFCBA), compared with NFA

Summary

Introduction

Due to its unique characteristics, e.g., high flowability, passing ability, and resistance to segregation, the use of Self-compacting concrete (SCC) has gained wide acceptance in recent years. 159 Page 2 of 13 site and the labour needed for concrete placement As it can flow under its own weight and maintain sufficient resistance to segregation, SCC has excellent applicability for elements with complicated shapes and congested reinforcement. As SCC possess a high cement content, the autogenous shrinkage becomes significant [5], because of the greater volume of small-diameter pores and the available water reduction [6]. This leads to potential early-age cracking, which is a big concern for service life. LWA releases water to the surrounding paste to replace moisture lost and reduce self-desiccation [10]

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Conclusion