Search

The primary cause of early-age cracking is high tensile stress resulting from restrained shrinkage of concrete structures. This study examined the shrinkage performance of polypropylene fiber reinforced concrete (PFRC) through restrained ring and free shrinkage tests. The impact of polypropylene fiber on shrinkage deformation and restrained shrinkage stress of concrete was analyzed. Furthermore, the mechanism of multi-scale polypropylene fiber to improve the crack resistance of PFRC was discussed. Test results demonstrated that adding polypropylene fiber to concrete significantly reduced the possibility of early cracking in concrete matrix. Plain concrete (A0) showed the highest potential for early-age cracking. At 28 days of age, the cracking risk factor of single-doped, double-doped, multi-doped polypropylene fiber reinforced concrete (A1, A2, and A3) was 0.851, 0.793, and 0.665, which decreased by 7.1%, 13.43%, and 27.4% compared with A0, respectively, suggesting the effect was better positive in reducing the crack risk when multi-scale polypropylene fiber hybridized. [ABSTRACT FROM AUTHOR]

To study the damage evolution behavior of polypropylene fiber reinforced concrete (PFRC) subjected to sulfate attack, a uniaxial compression test was carried out based on acoustic emission (AE). The effect of sulfate attack relative to time and fiber hybridization were analyzed and the compression damage factor was calculated using a mathematical model. The changes to AE ringing counts during the compression could be divided into compaction, elastic, and AE signal hyperactivity stages. In the initial stage of sulfate attack, the concrete micropores and microcracks were compacted gradually under external load and a corrosion products filling effect, and this corresponded with detection of few AE signals and with concrete compression strength enhancement. With increasing sulfate attack time, AE activity decreased. The cumulative AE ringing counts of PFRC at all corrosion ages were much higher than those for plain concrete. PFRC could still produce AE signals after peak load due to drawing effect of polypropylene fiber. After 150 d of sulfate attack, the cumulative AE ringing counts of plain concrete went down by about an order of magnitude, while that for PFRC remained at a high level. The initial damage factor of hybrid PFRC was −0.042 and −0.056 respectively after 150 d of corrosion, indicating that the advantage of hybrid polypropylene fiber was more obvious than plain concrete and single-doped PFRC. Based on a deterioration equation, the corrosion resistance coefficient of hybrid PFRC would be less than 0.75 after 42 drying-wetting sulfate attack cycles, which was 40% longer than that of plain concrete. [ABSTRACT FROM AUTHOR]

A nonlinear 3D FEM was developed for reproducing the three‐edge bearing test (TEBT) of pipes. The model was validated by considering the experimental results on standard reinforced concrete pipes (RCPs) and fiber‐reinforced concrete pipes (FRCPs) with 1000 mm internal diameter presented in the Part 1. The relative error between numerical simulation and laboratory test results for both the service (D0.3) and the ultimate (Du) D‐load (DL) were lesser than 2.1% and 6.3%, respectively. Additionally, a new structural design process that takes into consideration the geometric and mechanical variables involved into the TEBT of pipes, including the type and reinforcement configuration, is proposed. Because of applying this approach, design‐oriented tables with minimum steel‐cage reinforcement ratios for RCPs and FRCPs valid for pipes with inner diameters ranging from 300 mm to 1800 mm are established for the pipe strength classes I to V and wall thickness A, B, and C defined in the ASTM C76. Based on the numerical results, it can be confirmed that the hybrid use of basalt‐polypropylene fibers permits to reduce the steel reinforcement ratio respect to the equivalent RCP and, for some diameters and strength classes, the total elimination. These results represent a step forward in the use of fiber reinforced concrete in the pipe industry, which can lead to more durable and sustainable piping products. [ABSTRACT FROM AUTHOR]

An experimental program consisting in producing and testing reinforced concrete pipes (RCPs) under the three‐edge bearing tests considering different types of reinforcement was carried out. Four types of RCPs were produced, these reinforced with: (1) polypropylene macrofibers; (2) basalt microfibers; (3) combination of both (hybrid reinforcement); and (4) plain concrete. The analysis of the crack patterns and both service and ultimate mechanical responses allowed concluding that the use of fibers do not lead to an effective increase of the first cracking load; however, both types of fibers allowed a better crack width control respect to the standard RCP. In this regard, basalt microfiber reinforced concrete led to a better response caused by concentrated loads (jacketing) whilst polypropylene macrofibers increased the concrete pipe performance in terms of bearing capacity and flexural crack control. The hybrid fiber reinforced concrete was found to be the most suitable alternative for increasing the load bearing capacity and the crack width control for service loads. These incipient experimental results permit to conclude that this type of hybrid basalt‐polypropylene fiber reinforced concretes are an interesting alternative to traditional steel‐cage RCPs. [ABSTRACT FROM AUTHOR]

• BPFRC restrained shrinkage experiment study. • Exploring the enhancement mechanisms of crack resistance in BPFRC through SEM. • Evaluation of sensitivity index of crack resistance of BPFRC by grey relational theory combined with entropy weight method. In order to study the anti-crack mechanism of basalt-polypropylene fiber reinforced concrete (BPFRC), based on the restrained shrinkage test of BPFRC, the anti-crack enhancement mechanism of basalt fiber and polypropylene fiber was discussed through SEM microscopic test, and the sensitivity index of BPFRC's anti-crack performance was studied by combining grey relational theory and entropy weight method. The results show that basalt fiber has a significant inhibitory effect on the initiation and propagation of micro-cracks, and polypropylene fiber has a more obvious inhibitory effect on the propagation of macro-cracks. Mixing basalt fiber and polypropylene fiber into concrete can improve the pore structure of concrete matrix, reduce the initial defects of concrete matrix, enhance the density of the interface transition zone between aggregate and matrix, make concrete play a bridging role in different stages of stress deformation, and enhance the crack resistance of concrete more significantly. Grey relational theory combined with entropy weight method shows that the splitting tensile strength has the most significant influence on the crack resistance of BPFRC. This study can provide a new method for the sensitivity index analysis and crack resistance evaluation of concrete. [ABSTRACT FROM AUTHOR]