Microstructure of interface between fibre and matrix in 10-year aged GRC modified by calcium sulfoaluminate cement

Abstract

a b s t r a c tTime-dependent property changes in glass fibre reinforced cement (GRC) mainly result from a combination of the alkalinity of the matrix and densification of the matrix (e.g. due to calcium hydroxide precipitation) within and around the glass fibre strands. The microstructure of the interface between matrix and fibres in GRC has a significant impact on its durability. This paper describes a study of two GRC formulations (with OPC, and OPC plus calcium sulfoaluminate based matrices) aged for 10 years at 25°C. Thin-section petrography (TSP) and SEM are used to compare the microstructure of both polished surfaces and fractured surfaces. The aged OPC/ GRC demonstrates significantly brittle behaviour with substantial densification of C-S-H/CH intermixture occurring around glass fibres. In contrary, the aged composite made with the OPC plus calcium sulfoaluminate shows greatly retained toughness, accompanied by considerably flexible interfacial and interfilamentary areas around the glass fibres.

Durability of GFRC Modified by Calcium Sulfoaluminate Cement under Elevated Curing Temperatures

“…However, its long-term durability has aroused some concerns, which has limited its wider application in engineering. It was reported that GFRC suffered from severe strength reduction and ductility reduction as service life increases [4][5][6][7][8][9]. e exact mechanisms underlying this degradation process are still debated but it is normally accepted that it involves a combination of glass fibre corrosion caused by the hydroxyl in the pore solution [10,11] and significant CH precipitation between and around fibres that cause loss of flexibility [12].…”

“…Many research studies have been done to investigate the microstructural features and durability of GFRC modified by CSA cement (CSA/GFRC). Due to the limitation of long curing period in the laboratory, most of them are based on hot-water accelerated ageing [4,[17][18][19]. Purnell and Beddows [18] reported that after curing at 50°C for 140 d, there were almost insignificant changes which occurred in the mechanical performance of CSA/GFRC; with the progress of ageing until 316 d, composite ultimate tensile strength reduced from 30 MPa to 22 MPa, but the embedded fibres could still play an important role in bridging and limiting of cracking development.…”

“…Purnell and Beddows [18] reported that after curing at 50°C for 140 d, there were almost insignificant changes which occurred in the mechanical performance of CSA/GFRC; with the progress of ageing until 316 d, composite ultimate tensile strength reduced from 30 MPa to 22 MPa, but the embedded fibres could still play an important role in bridging and limiting of cracking development. Research by Song [4] showed that CSA/GFRC retained most of the toughness after ageing for 10 years at 25°C, accompanied by considerably flexible interfacial and interfilamentary areas around the glass fibres.…”

State-of-the-Art Review of Capabilities and Limitations of Polymer and Glass Fibers Used for Fiber-Reinforced Concrete

“…It is generally accepted that AR silica glass fibers mixed in cementitious matrices lose some of their reinforcing effectiveness over time because of their chemical sensitivity to the alkaline environment, as explained in the previous section [ 84 , 90 ]. In order to help improve the long-term performance of AR glass FRC, Song et al [ 91 ] investigated modifying the binder with a partial replacement of ordinary Portland cement with calcium sulfoaluminate cement. The study found that the proposed method greatly improves the long-term performance of the composites.…”

“…When dispersed in low volumes, nylon microfibers have minimal effects on the pre-crack mechanical properties. However, a higher toughness and a more ductile failure mode can be achieved with the addition of nylon fibers [ 91 , 182 , 183 , 184 ]. Zia and Ali [ 134 ] investigated the effects of addition of jute, nylon, and PP fibers on controlling the cracks.…”