Durability of ultra-high performance concrete – A review

Experimental study on the physico-mechanical properties and microstructure of foam concrete mixed with coal gangue

To reduce the adverse impact of coal gangue heaping and save natural resource, artificial coal gangue sands are utilized as fine aggregates in the concrete preparation. The mechanical and environmental properties of coal gangue sand concrete were studied experimentally and theoretically by considering concrete strength grades (C30, C50) and replacement ratios (0, 25%, 50%, 75%, 100%). The results show that coal gangue sand will weaken the adhesion performance of the transition zone between cement mortar and coarse aggregate. The elastic modulus and axial compressive strength of coal gangue sand concrete were decreased by increasing the replacement ratio regardless of concrete grade. When the replacement ratio is 100%, the elastic modulus and axial compressive strength of C30-grade concrete were reduced by 2.9% and 12.6% respectively whilst the values of C50-grade concrete were 5.0% and 21.5% respectively. Based on the tested results, the prediction formulas of the mechanical properties and the uniaxial compressive stress–strain model of the coal gangue sand concrete under different replacement ratio are proposed. Through life cycle assessment, it is found that the replacement ratio of the coal gangue sand is negatively correlated with environmental impact and willingness to pay (considering transport cost), and positively correlated with willingness to pay (without considering transport cost). The balance point is defined by the environmental influence of coal gangue sand concrete when the willingness to pay (considering transport cost) of coal gangue sand concrete under different replacement ratio is equal. According to the tested results, the prediction formula of the balance point under different transport distance is proposed. When the consistent transportation distance of gangue sand and natural sand exceeds 140 km, the utilization of coal gangue sand can produce good environmental benefits. 

Comparative study on mechanical and environmental properties of coal gangue sand concrete

Emergy-accounting-based comparison of carbon emissions of solid waste recycled concrete

Strength prediction and optimization for ultrahigh-performance concrete with low-carbon cementitious materials – XG boost model and experimental validation

Coal gangue (CG) represents a huge amount of industrial solid waste in China, and usually is used as a coarse aggregate to produce low-strength coal-gangue-based concrete. In this paper, in order to prove the possibility to obtain a higher-strength concrete with a higher CG utilization rate, reactive powder concrete (RPC) with coal gangue as a sand replacement at different replacement ratios was studied. RPC samples were prepared by replacing natural river sand (RS) with CG sand at different CG/RS weight ratios from 0–100% at intervals of 25%. Mechanical tests were carried out, and the microstructure features of RPC samples at 28 days were characterized. The test results showed that strong back shrinkage of strength existed. On days 7 and 14, the flexural strengths of samples with CG/RS replacement ratios of 0–75% fluctuated around the mean value. Strengths of samples with a CG/RS replacement ratio of 100% dropped off. However, on day 28, the flexural strengths of samples with CG were all lower than the strengths of samples on days 7 and 14. The flexural strengths and compressive strengths of the RPC with a CG/RS replacement ratio of 100% on day 14 were 14.09 MPa and 37.03 MPa, respectively, which decreased to 6.42 MPa and 28.44 MPa, respectively, on day 28. Compared with natural river sand, CG sand reduced the working performance, compressive strength, and flexural strength of RPC. Microscopic analysis showed that on day 28, increasing the CG replacement ratio could inhibit cement hydration, weaken the interface transition zone, and lead to the degradation of the RPC’s performance. Modification of CG sand would be helpful to obtain higher-strength concrete.

/pdf/mechanical-properties-of-reactive-powder-concrete-with-coal-3ruk297z.pdf

Mechanical Properties of Reactive Powder Concrete with Coal Gangue as Sand Replacement

Conventional properties, rheological properties, and storage stability of crumb rubber modified asphalt with WCO and ABS

Rheological properties and viscosity reduction mechanism of aromatic/naphthenic oil pre-swelling crumb rubber modified asphalt

In order to explore the influence of gradation and concentration on the rheological parameters of uncemented coal gangue-fly ash backfill (UCGFB) slurry, based on the fractal theory, the particle size distribution of the mixture of coal gangue and fly ash under different mixing ratios are analyzed in this paper. On this basis, the influence of gradation and concentration on rheological parameters of UCGFB slurry are studied and a numerical simulation of slurry transportation is also carried out. The results show that (1) the fractal dimension can well characterize the grading characteristics of UCGFB mixtures, the larger the fractal dimension, the more fine particles in the material. (2) The fractal dimension of 2.628 is a critical point, when the fractal dimension of the mixture is greater than or equal to 2.628, the content of fine particles in the slurry can meet the requirements. On this basis, by adjusting the concentration of the slurry, the slurry can reach a good state. (3) When the slurry concentration reaches 79%, no matter how the gradation of the mixture changes, the rheological parameters of the slurry are at a high level. (4) In this paper, the average pressure loss per unit length pipeline is between 3000–8000 Pa for slurry with different mixing ratios, with a minimum value of 3070 Pa and the maximum value of 7697 Pa. Moreover, the pressure loss of bend is greater than that of straight pipe.

/pdf/study-on-rheological-characteristics-of-uncemented-coal-lv4h8bfh.pdf

Study on Rheological Characteristics of Uncemented Coal Gangue-Fly Ash Backfill (UCGFB) Slurry Based on Fractal Theory

Understanding the mechanical properties and failure process of cemented paste backfill with recycled rubber (RCPB) is the foundation of backfill design in underground mining. In this study, physical and mechanical tests were conducted on RCPB to obtain its mechanical property parameters, such as its uniaxial compressive strength (UCS), toughness, and peak strain. The influence of the rubber dosage on the mechanical properties of RCPB was also analyzed. In addition, the deformation behavior, fracture development, and failure process of RCPB with different rubber contents were observed using the digital image correlation (DIC) technique. The experimental results suggested that, although the UCS of RCPB is reduced as more rubber is added, its toughness and ability to absorb energy is increased. Moreover, the impact resistance of RCPB is improved by this increased toughness. With the increase in the rubber content, the deformation corresponding to the plastic yield stage of RCPB increased, which resulted in better ductility and improved impact resistance. The failure of the RCPB specimens mainly showed an “X” shape. The results of this study help us to better understand the mechanical behavior of RCPB after backfilling underground.

/pdf/the-failure-mechanical-properties-of-cemented-paste-backfill-3ibgx0ny.pdf

The Failure Mechanical Properties of Cemented Paste Backfill with Recycled Rubber

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