Fracture Properties and Restrained Shrinkage Cracking Resistance of Cement Mortar Reinforced by Recycled Steel Fiber from Scrap Tires

Semicircular bending fracture test to evaluate fracture properties and ductility of cement mortar reinforced by scrap tire recycled steel fiber

Axial compressive behavior of environmentally friendly high-strength concrete: Effects of recycled tire steel fiber and rubber powder

The effects of nano zinc oxide (ZnO) and nano reduced graphene oxide (RGO) on moisture susceptibility property of stone mastic asphalt (SMA)

ABSTRACT: Recycled steel fiber processed from waste tires were used to prepare ultra-highperformance concrete. Ultra-high-performance concrete with normal commercial steel fiber and plain concrete without any steel fiber were also prepared for comparison. Experimental investigations were conducted to determine the mechanical properties of ultra-high-performance concretes, including compressive strength, splitting tensile strength, fracture energy and elastic modulus. Additionally, explosive spalling of concretes was also tested via exposure to high temperature up to 800◦C. The recycled tire steel fiber could improve the fracture energy of concrete more significantly than normal commercial steel fiber. The splitting tensile strength of the recycled tire steel fiber reinforced concrete was also the highest among these concretes with various steel fiber. Moreover, the recycled steel fiber presented better behavior to resist the explosive spalling of the ultra-high-performance concrete. It is concluded that the recycled tire steel fiber help ultra-highperformance concrete possess higher toughness in terms of fracture energy and higher cracking resistance, so as to exhibit higher resistance to thermally explosive cracking.

Fracture behavior of environmentally friendly high-strength concrete using recycled rubber powder and steel fibers: Experiment and modeling

The use of nanomaterials has brought about a huge revolution in the development of various industries. Moreover, in the pavement industry, researchers have been applying nanomaterials for many years due to their unique properties to enhance the features of asphalt mixtures and increase their resistance to various failures. In this study, nanographene oxide (GO) has been used in the amount of 0.2, 0.5, and 0.8 percent of consumed bitumen to improve the low-temperature cracking resistance and the high-temperature rutting resistance of hot-mix asphalt (HMA). For this purpose, to examine the impact of this material on the HMA, the semicircular bending (SCB) fracture test and Hamburg wheel tracking (HWT) test were applied. In addition, conventional bitumen tests were performed to investigate the impact of nanoGO on virgin bitumen in this study. The outcomes of conventional bitumen experiments displayed that the addition of nanoGO to pure bitumen augments viscosity, specific gravity, and softening point and reduces the penetration and ductility of pure bitumen. Furthermore, outcomes of the SCB fracture test indicated that nanoGO enhances the stress intensity factor (SIF) of the asphalt mixture and improves the low-temperature cracking resistance of asphalt specimens. Moreover, the addition of nanoGO to the asphalt mixture increased rutting resistance and decreased rutting depth. In addition, the results of the ANCOVA statistical analysis demonstrated the significant effect of this nanomaterial on the improvement of the low-temperature cracking resistance and the rutting resistance of HMA.

Evaluation of the impact of long-term aging on fracture properties of warm mix asphalt (WMA) with high RAP contents

In the current investigation, the effect of recycled steel fibers recovered from waste tires on the pull-out response of ribbed steel bars from carbon nanotube (CNT)-modified ultrahigh performance fiber reinforced concrete (UHPFRC) was considered using the multiscale finite element method (MSFEM). The MSFEM is based on three phases to simulate CNT-modified UHPC, recycled steel fibers (RSFs), and ribbed steel bars. For the first time, a bar ribbed has been simulated to make more realistic assumptions, and RSFs have been distributed in the form of curved cylinders of different lengths and with a random distribution within a concrete matrix. The interaction of the steel bar and the RSFs with the concrete is applied by the cohesive zone model (CZM). After confirming the simulation outcomes with the experimental results, the steel bar pull-out response is investigated using load-slip curves. The impact of the CNT content, RSFs and their aspect ratio on the bond strength of steel bars and CNT-modified UHPFRC was assessed. The results show that using RSFs with a lower aspect ratio (steel microfibers) significantly improves the pull-out characteristics of steel bars from concrete. Accordingly, the proposed MSFEM is considered for simulating the effects of different parameters on the pull-out response of ribbed steel bars from concrete without causing complex, time-consuming, or costly experiments. The results indicated that waste fiber or RSF can be used as a toughening component in CNT-modified ultrahigh-performance concrete and as a replacement for industrial steel fibers.

Effect of inclusion of natural pozzolan and silica fume in cement - based mortars on the compressive strength utilizing artificial neural networks and support vector machine

There is a lack of reliable carbon dioxide emissions factors (CDEFs) for recycled steel fiber (RSF) and quantitative studies assessing the carbon dioxide emissions (CDE) of ultra high performance concrete (UHPC) made with RSF (RSF-UHPC). Combined with experimental research and life cycle evaluation methods, the effects of key fiber parameters, strength, process, and material components on the mechanical properties and CDE of UHPC were studied. The results indicate that RSF-UHPC exhibited better flowability and comparable compressive strength and tensile strength to UHPC made with industrial steel fiber (ISF-UHPC) for the same fiber dosage. This is attributed to short fibers reducing the loss of flowability and the fibers helping to halt or slow the propagation of microcracks in RSF-UHPC. UHPC with 2% RSF is also more environmentally friendly, with calculated CDE of 929.64 kgCO2e/m3 and a CDE intensity of 8.03 kgCO2e/(m3 · MPa), which are, respectively, 23.91% and 18.1% lower than those of ISF-UHPC (for the same fiber dosage of 2%). Based on a life cycle assessment, the CDEF of RSF was determined to be 0.587 kgCO2e/kg. Furthermore, the CDE during the raw material acquisition stage are the primary contributors to the total CDE of UHPC, with cement and fibers being the main factors.

Experimental investigations on the mechanical properties of ultra-high performance concrete (UHPC) incorporating two types of recycled steel fiber processed from waste tires and three types of industrial steel fiber were carried out for comparison. Mechanical properties of UHPC include compressive strength, splitting tensile strength, fracture energy, and elastic modulus. Their explosive spalling behaviors under high temperatures were also investigated. The results show that all types of steel fiber exhibit a beneficial effect on the mechanical properties and the anti-spalling behavior of UHPC, except that recycled steel fiber with rubber attached (RSFR) has a slightly negative effect on the compressive strength of UHPC. Compared to industrial steel fibers, recycled steel fibers have a more significant influence on improving the splitting tensile strength and fracture energy of UHPC, and the improvement of RSFR was much higher than that of recycled steel fiber without rubber (RSF). UHPC that incorporates industrial hooked-end steel fiber (35 mm in length and 0.55 mm in diameter) exhibits the best resistance to explosive spalling, and the second is the RSF reinforced UHPC. The positive relationship between the fracture energy and the anti-spalling behavior of steel fiber reinforced UHPC can be presented. These results suggest that recycled steel fiber can be a toughening material and substitute for industrial steel fibers to be used in ultra-high performance concrete, especially RSFR.

Effect of utilising ferrosilicon and recycled steel fibres on ultra-high-strength concrete containing recycled granite

According to a recent estimate, over 1.5 billion wasted tyres which containing over 40% of vulcanised rubber and 15% of steel fibre are discarded yearly, which posing a serious threat to circular economy implementation and transition to net zero. To minimise the greenhouse gas(GHG) emission and the environmental side effect caused by burning and burying these waste tyres, recycling and reusing these materials for sustainable structural designs has become the centre of attention. This paper focuses on applying recycled bead steel fibre to improve the shear capacity of fibre-reinforced concrete beams. Moreover, the existing national standard known as Eurocode 2 and TR63 can hardly illustrate the relationship between fibre and high-strength concrete. This study is the first to investigate shear behaviours of high-strength industrial and recycled steel fibre reinforced concrete beams with consideration of different shear span ratios. Therefore, twenty real-scale beams are constructed to examine the shear capacity of high-strength industrial and recycled steel-fibre reinforced concrete beams, which aims to compare the improvement of shear strength through experiments and identify different shear strength improvements of the two categories of steel fibre. Besides, comprehensive data of 164 beams from previous studies have been collected to benchmark with the experimental results for the formula design. This study proves the feasibility of replacing industrial steel with recycled steel fibre to improve the shear capacity of fibre-reintroduced concrete beams. Moreover, there are six novel equations designed developed using Eurocode 2 and TR63 as a basis in this study. Based on the findings of the paper, the proposed formulas demonstrate remarkable accuracy, with an average value of 0.982 and standard deviation of 0.213, respectively. Following an exhaustive comparison of RSF and ISF reinforced concrete beams, with a focus on economic expenditure and GHG emissions, it can be concluded that RSF offers superior economic and environmental benefits, which reduce the emissions up to 25.39% and price up to 28.04% when replacing ISF 0.8% RSF, respectively.

This study’s goal is to establish systematic multiscale equations to estimate the compressive strength of cement mortar with a high volume of lime (L) and to be used by the construction industry with no theoretical restrictions. For that purpose, a wide tested data and the data gathered in the literature (a total of 392 tested cement mortar modified with lime) have been statically analyzed and modeled. The lime content ranged from 0 to 45% (by cement weight). Depending on literature data the w/c ranged from 0.3 to 0.74, the w/c of 0.5 was selected for this research. The compressive strength of lime-modified cement mortar for up to 28 days ranged from 3 to 75 MPa. The compression strength of the cement mortar reduced with an increasing percentage of lime. The linear and nonlinear regression, M5P-tree, and artificial neural network (ANN) technical approaches were used for the qualifications. In the modeling process, the most relevant parameters affecting the compression strength of cement mortar, i.e. lime (L) incorporation ratio (0–45% of cement’s mass), water-to-cement ratio (0.3–0.74), and curing ages (1 to 28 days). According to the statistical assessment such as R, MAE, and RMSE, the compression strength of cement mortar can be predicted very well in terms of water-to-cement ratio, lime content, and curing age using various simulation techniques. The maximum and minimum error between the actual test results and the outcome of the prediction using NLR and ANN (training dataset) were 0.01–21 MPa and 0.012–9 MPa, respectively, and ranged between 0.03 and 14 MPa and 0.02 and 6 MPa errors, respectively, in terms of tested data. The margin of error in using the nonlinear regression-based model (NLR) and ANN for the training dataset was 1.41 and 1.92, respectively, and it was 2.26 and 2.44 respectively in using the tested dataset. The outcomes of this paper suggest that the nonlinear regression-based model (NLR) and ANN are performing better than other applied models using training and testing datasets. The result of the sensitivity investigation was the curing period that is the highest dominating value for the prediction of the compressive strength of cement mortar.

Development of reactive powder concrete with recycled tyre steel fiber