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Mechanical Properties and Microstructure of Polypropylene Fiber Reinforced Cement Mortar Soil
Bo Ruan,Hui Ding,Jidong Teng,Wei Deng,Shilong Zheng,Chenxi Ruan 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.6
A series of unconfined compressive strength tests and flexural strength tests are carried out to evaluate the improved effect of polypropylene fiber on the defects of cement mortar soil. The following factors, including the fiber content, cement content, sand content and curing age, are studied to investigate the influences on the mechanical properties and microstructure of the samples. The results show that the unconfined compressive strength (UCS), residual strength and flexural strength of the fiber reinforced cement mortar soil (FRCMS) substantially increase with increasing fiber content. The peak strain and ratio of the flexural-compression strength (Rfcs) of the FRCMS first increase and then decrease with an increase in fiber content,and the optimal fiber content is 3.5%. The brittleness index of the FRCMS is found to be inversely proportional to fiber content. The results suggest that the addition of an appropriate amount of fibers can substantially improve the plasticity and lateral stress capacity of the FRCMS. The strength of the FRCMS improves with the increase in cement content, sand content and curing age within a certain range. The microstructure of the FRCMS are analyzedby scanning electron microscopy (SEM) tests.
Jinkun Sun,Rita Yi Man Li,Lindong Li,Chenxi Deng,Shuangshi Ma,Liyun Zeng Techno-Press 2023 Advances in concrete construction Vol.15 No.5
Fast infrastructure development boosts the demand for shotcrete. Despite sand and stone being the most common coarse and fine aggregates for shotcrete, excessive exploration of these materials challenges the ecological environment. This study utilized an industrial solid waste, high-titanium heavy slag, blended with steel fibers to form Wet Shotcrete of Steel Fiber-reinforced High-Titanium Heavy Slag (WSSFHTHS). It investigated its workability, shotcrete performance and mechanical properties under different water-to-cement ratios, fly ash content, superplasticizer dosage, and steel fiber content. The tunnel excavation and support were investigated by conducting finite element numerical simulation analysis and was used in 3 tunnel lining pipes in Zhonggouwan tailing pond. The major findings are as follows: (1) The water-to-cement ratio (w/c ratio) significantly impacted the compressive strength of WSSFHTHS. The highest 28-day compressive strength of 60 MPa was achieved when the w/c ratio was 0.38; (2) Adding fly ash improved the workability and shotcrete performance and strength development of WSSFHTHS. The best anti-permeability performance was achieved when the fly ash constituted 15%, with the lowest permeability coefficient of 4.596 × 10-11 cm/s; (3) The optimum superplasticizer dosage for WSSFHTHS is 0.8%. It provided the best workability and shotcrete performance. Excessive dosage resulted in water bleeding and poor aggregate encapsulation, while insufficient dosage decreased flowability and adversely affected shotcrete performance; (4) The dosage of steel fibers significantly impacted the flexural and tensile strength of WSSFHTHS. When the steel fiber dosage was 45 kg/m<sup>3</sup>, the 28-day flexural and tensile strengths were 8.95 MPa and 6.15 MPa, respectively; (5) By integrating existing shotcrete techniques, the optimal lining thickness was 80 mm for WSSFHTHS per simulation. The results revealed that after using WSSFHTHS, the displacement of the tunnel surrounding the rock significantly improved, with no cracks or hollows, similar to the simulation results.