Engineering, Mechanical and Dynamic Properties of Basalt Fiber Reinforced Concrete

Mechanical properties and acoustic emission characteristics of basalt fiber reinforced cemented silty sand subjected to freeze-thaw cycles

Freeze-thaw (F-T) cycling poses a significant challenge in seasonally frozen zones, notably affecting the mechanical properties of soil, which is a critical consideration in subgrade engineering. Consequently, a series of unconfined compressive strength tests were conducted to evaluate the influence of various factors, including fiber content, fiber length, curing time, and F-T cycles on the unconfined compression strength (UCS) of fiber-reinforced cemented silty sand. In parallel, acoustic emission (AE) testing was conducted to assess the AE characteristic parameters (e.g., cumulative ring count, cumulative energy, energy, amplitude, RA, and AF) of the same material under F-T cycles, elucidating the progression of F-T-induced damage. The findings indicated that UCS initially increased and then declined as fiber content increased, with the optimal fiber content identified at 0.2%. UCS increased with prolonged curing time, while increases in fiber length and F-T cycles led to a reduction in UCS, which then stabilized after 6 to 10 cycles. Stable F-T cycles resulted in a strength loss of approximately 30% in fiber-reinforced cemented silty sand. Furthermore, AE characteristic parameters strongly correlated with the stages of damage. F-T damage was segmented into three stages using cumulative ring count and cumulative energy. An increase in cumulative ring count to 0.02 × 104 times and cumulative energy to 0.03 × 104 mv·μs marked the emergence of critical failure points. A sudden shift in AE amplitude indicated a transition in the damage stage, with an amplitude of 67 dB after 6 F-T cycles serving as an early warning of impending failure.

Influence of Polymer Fibers on the Structure and Properties of Modified Variatropic Vibrocentrifuged Concrete

The application of polymer materials in concrete structures is widespread and effectively used. However, there is a lack of a systematic knowledge base about the structure formation and properties of variatropic vibrocentrifuged modified fiber-reinforced concrete. The purpose of this work is the investigation of the influence of polypropylene (PF) and basalt fiber (BF) and modification with microsilica (MS) on the properties of variatropic concretes obtained using the synthesized vibration centrifugation technology. Test samples were made using vibration centrifugation technology, followed by sawing. Various types of fiber reinforcement were studied, both individually and in combination. To determine the degree of effectiveness of each recipe solution, the following main characteristics were monitored: the density and workability of concrete mixtures; the density of hardened composites; compressive strength (CS); bending strength (BS); water absorption (WA). In variatropic vibrocentrifuged concrete, the greatest efficiency is achieved with dispersed BF reinforcement in an amount of 1.5%. Compared to the control composition, the increase in CS was 8.50%, the increase in BS was 79.17%, and WA decreased by 27.54%. With PF reinforcement, the greatest effect was recorded at a dosage of 1.0%. The increase in CS was 3.16%, the increase in BS was 10.42%, and WA decreased by 17.39%. The MS modification showed the best effect with 8% replacement of part of the Portland cement. The increase in CS was 17.43%, the increase in BS was 14.58%, and WA decreased by 33.30%. The most effective and economically rational formulation solution for vibrocentrifuged concrete is combined fiber reinforcement in combination with the MS modification in the following quantities: BF-1.0%; PF-0.5%; MS-8%. The increase in CS was 22.82%, the increase in BS was 85.42%, and WA decreased by 37.68%.

An Experimental Study on the Properties of Concrete and Fiber-Reinforced Concrete in Rigid Pavements

The complex effect of the amount of cement, polypropylene fiber (the fiber length was 39 mm, and the diameter was 0.45 mm), and polycarboxylate superplasticizer on concrete properties for rigid pavement was determined using the methods of experiment planning and experimental-statistical modeling. The fluidity of all the mixtures was S1. The W/C of the mixtures depended on the composition of the concrete and variable from 0.32 to 0.46. It was found that, by increasing the amount of superplasticizer from 1% to 1.8-2%, the compressive strength of concrete increased by 4.5-6 MPa after 3 days and by 7-9 MPa after 28 days. The flexural strength in this case increased by 0.6-0.9 MPa. The use of polypropylene fiber in the amount of 1.5-1.8 kg/m3 increased the compressive strength of concrete by an average of 3 MPa, increased the flexural strength by 0.5-0.6 MPa, reduced the abrasion capacity by 9-14%, and increased the frost resistance by up to 50 cycles. When using a rational amount of superplasticizer and fiber, the compressive strength of concrete, even with a minimum cement amount of 350 kg/m3, was at least 65 MPa, its flexural strength was at least 6 MPa, its frost resistance was F200, and its abrasion capacity was not more than 0.30 g/cm2. Concrete with such properties can be used for roadways of any type. Low abrasion capacity and high frost resistance provide the necessary durability of concrete for rigid pavement during operation.

Research into Preparation and Performance of Fast-Hardening RPC Mixed with Straw

Based on its characteristics of early strength, good toughness, and excellent mechanical and impact resistance, steel fiber-reinforced fast-hardening reactive powder concrete (RPC) is expected to become an alternative material used in the rapid repair of marine concrete structures. However, the steel fibers have also caused corrosion problems in coastal environments. To make doped fiber fast-hardening RPC more adaptable for use in ocean engineering, this study prepares fast-hardening RPC mixed with straw and studied the effects of straw content and curing age on its slump flow, setting time, and mechanical performance (flexural strength, compressive strength, and flexural toughness). The effects of straw addition on the compactness and hydration products of fast-hardening RPC were studied through macro- (ultrasonic analysis) and micro-scopic analysis (electron microscopy scanning and X-ray diffraction patterns). The straw content mentioned in this paper refers to the percentage of straw in relation to RPC volume. The results showed that straw reduced the fluidity of RPC slurry by 10.5-11.5% compared to concrete without straw, and it accelerated the initial setting of RPC slurry. When the straw content accounted for 1% of RPC volume, the setting rate was the fastest, with a increasing rate being 6-18%. Compared to concrete without straw, the flexural and compressive strength of fast-hardening RPC was enhanced by 3.7-30.5%. When the content was either 3% or 4%, the mechanical properties improved. Moreover, when the straw content accounted for 4% of RPC volume, the flexural toughness was the highest, with the increase rate being 21.4% compared to concrete without straw. Straw reduces the compactness of fast-hardening RPC.

Efficient, Fine-Grained Fly Ash Concrete Based on Metal and Basalt Fibers

This article presents the results of a study of the physical and mechanical properties of fine-grained fly ash concrete based on a combined reinforcement with steel and basalt fibers. The main studies were conducted using mathematical planning of experiments, which allowed the experiments to be algorithmized in terms of both the amount of experimental work and statistical requirements. Quantitative dependences characterizing the effect of the content of cement, fly ash binder, steel, and basalt fiber on the compressive strength and tensile splitting strength of fiber-reinforced concrete were obtained. It has been shown that the use of fiber can increase the efficiency factor of dispersed reinforcement (the tensile splitting strength to compressive strength ratio). To increase the resistance of basalt fiber, it is proposed to use fly ash in cement systems, which reduces the amount of free lime in the hydrating cement environment.