Study on the mechanical and shrinkage performance of POM-UHPC for stone masonry structure reinforcement

Ultra-high performance concrete (UHPC) is a promising cementitious engineering material with superior mechanical properties, which is an ideal potential rehabilitation material for stone masonry structures. However, the significant tensile stress generated from the UHPC overlay shrinkage under stone constraint is likely to have an adverse effect on rehabilitation. In this study, the development of workability, mechanical properties and shrinkage behavior of polyformaldehyde-UHPC (POM-UHPC) were investigated. The results showed that the optimum limestone powder content, POM fiber volume, water-binder ratio, and superplasticizer content in UHPC with excellent mechanical properties is about 40 %, 2 %, 0.19, 1.5 %, respectively. The increase of POM fiber volume and the decrease in water-binder ratio are beneficial to the development of mechanical properties while decreasing flowability. The autogenous shrinkage of UHPC is characterized by rapid growth in the early age, which could be mitigated by increasing the levels of water-binder ratio, limestone powder, POM fiber volume, and superplasticizer. The autogenous shrinkage development is positively correlated with the compressive strength. The increment of overlay thickness and stone surface roughness can reduce the constraint shrinkage of UHPC. The analyzed shrinkage-induced interfacial stresses between UHPC and stone increase with the UHPC layer thickness and the stone groove depth.