An investigation of the engineering properties and environmental impact of low-temperature modified electrolytic manganese residue for karst grouting materials.

To investigate the effects of different water-cement ratios and carbon fiber content on the compressive and splitting tensile strength of concrete, this experiment was designed with four water-cement ratios and four carbon fiber contents. The four water-cement ratios were 0.35, 0.38, 0.41, and 0.44, while the four carbon fiber contents were 0%, 0.3%, 0.6%, and 0.9%. The experimental results showed that: 1. The compressive strength and splitting tensile strength of concrete initially increased and then decreased with the increase in water-cement ratio and carbon fiber content, reaching their maximum when the water-cement ratio was 0.38; 2. When the carbon fiber content exceeded 0.3%, the uneven distribution of carbon fibers within the concrete weakened the interfacial bonding properties, thereby reducing the strength of the concrete.

To study the influence of different water-cement ratios and graphene oxide doping amounts on the mechanical properties of concrete. In this test, graphene oxide concrete with 4 water-cement ratios (0.35, 0.38, 0.41, 0.44) and six graphene oxide dopings (0, 0.02%, 0.04%, 0.06%, 0.08%, 0.1% (cement mass)) were prepared for mechanical properties. The results show that graphene oxide has a significant enhancement effect on the mechanical properties of concrete. As the water-cement ratio increases, the compressive strength and splitting strength of concrete show parabolic changes that first rise and then fall. Under the condition of water-cement ratio of 0.38, the concrete performance when graphene oxide dosages of 0, 0.02%, 0.04%, 0.06%, 0.08% and 0.1% were tested, and the compressive strength was increased by 10.11%, 15.81%, 22.78%, 30.04% and 24.48%, respectively, and the split tensile strength was increased by 3.87%, 6.25%, 18.75%, 27.97% and 22.02%, respectively. When the graphene oxide doping amount is 0.08%, the mechanical properties of the test piece are optimal.

The neutralization model of concrete corroded by CO₂ and SO₂ coupling was established. The model considered the dissolution process of solid calcium in concrete and the expansion damage caused by sulfation products. The influence of different water-cement ratios (0.37, 0.47, 0.57) on the neutralization process of concrete was studied. The changes of neutralization degree, gas diffusion coefficient, porosity, CaCO₃ content and CaSO₄ content of corroded concrete were analyzed. The results showed that with the increase of water-cement ratio, the diffusion range of CO₂ gas in concrete gradually increased, while the diffusion range of SO₂ was almost the same. After 28 days of corrosion, with the decrease of the water-cement ratio of concrete, the decrease in porosity of concrete increased gradually, and the expansion damage in concrete with different water-cement ratios was almost the same. In the area of increasing porosity, the change trends of concrete porosity were similar. With the increase of the water-cement ratio, the length of the complete sulfation area of concrete increased, the length of the partial sulfation area decreased, and the length of the partial carbonation area of concrete gradually increased.

The spatiotemporal evolution of multiple key layers overlying strata in thick coal seam has always been one of the key and difficult problems to be solved in the field of stratified filling, and the confined compression characteristics of fly ash slurry are the main influencing factors. In this paper, the lateral compression and viscosity test of filling materials were carried out, and the shear stress and plastic viscosity of filling materials were studied. The results show that the strain of fly ash in the initial stage of compaction accounts for 64.8% of the final strain. When the fly ash slurry is pressed, the stress increases exponentially with the strain, and the volume weight has a logarithmic relationship with the compaction stress. Both shear stress and plastic viscosity decrease negatively with the increase of water-cement ratio. When the ratio of fly ash to water to cement is controlled between 1.2 and 1.4 and the mass concentration is controlled between 41.7% and 45.5%, the slurry fluidity, pumpability and grouting efficiency are high.

It is well known that Portland cement has long been used in the construction of oil and gas wells. In this case, cementing slurries based on Portland cement are placed in the annular space, and after setting, they provide long-term isolation of the formations for subsequent operation. Therefore, the cementing process and the quality of these operations are of significant importance. To minimize of complications due to circulation loss, effective lightweight additives, including microspheres and microsilica, are widely used. However, when using microspheres, they may float when the water-cement ratio increases, and the resulting slurries exhibit high water yield. Microsilica in the cement slurry reduces water yield and does not float, but it thickens the slurry. The aim of this work is to develop lightweight cementing slurries for moderate temperatures with the rational use of the aforementioned additives. The authors of this article have developed a composition of lightweight cementing slurries for various climatic conditions using these additives. It has been specifically demonstrated that by adding 10% microspheres and 10% microsilica, effective lightweight cementing slurries can be obtained, where the various properties of the additives produce a positive outcome. The addition of 0.1% anhydrous sodium silicate to the cement slurry further improves the primary technological parameters of the slurry and, in general, the cement stone. Based on the conducted studies, an increase in the compressive strength of the cement stone to 7.04 MPa with a water-cement ratio of 0.7 was observed. Keywords: cement; microsphere; microsilica; lightweight; slurry.

Chemical shrinkage characteristics and prediction model of desulfurization electrolytic manganese residue-cement composite slurries

Abstract: Pervious concrete has varieties of names such as porous concrete, permeable concrete, no fines concrete and porous pavement. It is a special type of concrete with high permeability rate with porosity used for roadways applications that allows water from precipitation and other sources to pass directly through thereby reducing the runoff from a site and allowing recharge. The present research concentrates about bringing out the most efficient porous concrete by varying water cement ratios and size of aggregate. The main properties studied include porosity, compressive strength and water permeability. These properties were compared with those for conventional concrete. Although water permeability is the most important characteristic of the pervious concrete, there is no well-established method for its quantification. Therefore, an experimental procedure to assess the water permeability of pervious concrete is developed. Fine Pervious concrete is considered as FPC, Coarse Pervious concrete is considered as CPC, Nominal Pervious concrete is considered as NPC. Water cement ratios used are 0.28, 0.30, 0.32 and 0.34. It is observed that out of all varying water cement ratios from 0.28 to 0.34, FPC 3 got the highest compressive strength and later it decreased. CPC 2 got the highest compressive strength and later it decreased. NPC 1 got the highest compressive strength and later it decreased. However there is a lot of deviation in compressive strengths from grade of concrete since it is pervious concrete. It looks clear that with increase in water cement ratio there is decrease in Porosity percentage and permeability.

Steady pressure grouting exhibits the problems of low efficiency and uneven penetration. Therefore, this paper proposes a novel high-frequency pulsating grouting method to improve these problems. Through extensive experimentation and numerical simulations, the impact of pulsating parameters (grouting frequency, pressure amplitude), soil parameters (porosity, particle size), grouting pressure, water–cement ratio, and slurry rheological parameters on slurry penetration is investigated. The results indicate that the stone body grouted by the pulsating pressure is significantly more uniform and has longer penetration distances. During steady pressure grouting, as the grouting pressure or the water–cement ratio increases, the slurry is more prone to flow upward along the interface between the grouting pipe and the soil, which makes the grouted body uneven. When high-frequency pulsating grouting is employed, the slurry tends to flow into the soil, resulting in a more uniform grouted body. In the operating conditions described in this paper, the optimal pulsating frequency is around 3–4 Hz, and the optimal pulse amplitude is approximately 60% of the constant pressure. The results also show that the pulsating grouting method can increase the width by up to 68%. With the increase in porosity and particle size, the percentage of distance increase first increases and then decreases. The percentage of distance increase increases with the increase in viscosity and decreases with the increase in the Bingham rheological parameters (μp and τ0). This implies that the pulsating grouting needs certain resistance conditions to achieve optimal penetration performance. The mechanism of pulsating grouting is also analyzed. Pulsating pressure can clear blocked particles and lead to more uniform penetration of the slurry. This study can provide reference for the development of new grouting methods and equipment.

To study the compressive performance of rubberized concrete, 270 rubberized concrete specimens were designed using the equal-volume replacement method with different water-cement ratios, rubber contents, and rubber particle sizes, followed by cube compressive strength tests.Through analysis of the internal structure, failure modes, test phenomena, and failure mechanisms of the specimens, the impact and patterns of three variables on the compressive strength of concrete were summarized. The results show that the incorporation of rubber particles impact the internal pore structure of concrete, altering the distribution and impactive density of the cementitious material paste, which directly impacts its strength and elastic modulus. As the water-cement ratio increases, the impact of rubber content on the compressive strength of rubberized concrete cubes gradually decreases. With an increase in rubber particle content, the compressive strength of rubberized concrete gradually decreases. As the particle size of rubber particles increases, the interface area between rubber and the cement matrix increases, but due to the weaker bond between the rubber surface and the cement matrix, the macroscopic strength of rubberized concrete decreases. However, an increase in the particle size of rubber particles can lead to an increase in the compressive strength of rubberized concrete. The research results are expected to provide a theoretical basis for the practical application of rubberized concrete.

Study on the performance of sealing slurry at the bottom of geomembrane composite vertical cut off walls

Experimental study on ultra-early tensile creep of cement paste

As a kind of composite material, concrete plays an important role in underground geotechnical engineering such as mine grouting and support. At present, when it is subjected to external loads, the research mainly focuses on the influence of the ratio on the peak strength [1-2], Poisson 's ratio [3], permeability Chang et al. [4] made four kinds of high-porosity concrete with different proportions. After uniaxial compression of concrete, it was found that the peak strength of concrete decreased with the increase of water-cement ratio. Wu et al. [5] found that the flexural strength of rubber concrete increased with the decrease of water cement ratio. Song Hui et al A series of studies have found that the change of the ratio has an important influence on the mechanical properties of concrete As one of the important mechanical properties of concrete, the ductility of concrete can significantly affect the stability of concrete, and the stability is a key index to evaluate the application life of concrete in engineering. In the uniaxial compression test, the commonly used definition methods of brittleness ductility index mainly include brittleness index based on strength characteristics [8-10], brittleness index based on full stress-strain curve Wang Xuebin et al.

The water-cement ratio is one of the key parameters of grouting materials, which greatly affects the working performance and mechanical properties of grouting materials. This paper studies the physical properties, such as density, fluidity, consistency, bleeding rate, and stone rate, and the mechanical properties of flexural and compressive strength of micro-cement grouting materials with a water-cement ratio of 0.8:1, 1:1, 1.5:1 and 2.0:1 are investigated through a variety of indoor experiments. The results show that with the gradual increase of water-cement ratio, the density, consistency value, stone rate, flexural strength, and compressive strength of micro-cement grouting material gradually decrease, while the fluidity and bleeding rate of micro-cement slurry gradually increases. Although the slurry with a water-cement ratio of 1.5:1 and 2:1 has good fluidity, the high bleeding rate and the low stone body strength result in more water injected into the reinforced formation and low reinforcement strength. On the contrary, the slurry with a water-cement ratio of 0.8:1 has a low bleeding rate and high stone body strength, but low fluidity. The grouting performance and mechanical properties of the slurry with a water-cement ratio of 1:1 are relatively balanced. This study provides a basis for the subsequent on-site ultra-fine cement grouting project. A reasonable water-cement ratio can be selected according to the specific needs to ensure the reinforcement quality and safety of the grouting operation.

Experimental study on expansion and cracking properties of static cracking agents in different assembly states

Abstract In this paper, the double‐side direct shear experiments on the specimens with and without grooves were conducted to measure the shear load‐deformation curves of steel fiber‐reinforced concrete containing recycled coarse aggregate (SFRCA). The evaluation method for shear toughness was proposed first, and then the effects of water–cement ratio, replacement ratio of recycled coarse aggregate, volume content of steel fibers, and shear section height on the shear toughness of SFRCA were experimentally analyzed. The results showed that the proposed shear toughness evaluation method could reflect the shear toughness of SFRCA. The effects of the replacement ratio of recycled coarse aggregate and the volume content of steel fiber on the shear toughness of specimens with grooves had the same trend as those of specimens without grooves. The shear toughness ratio of SFRCA increased with the increase of the volume content of steel fibers, and decreased with the increase of water cement ratio and the replacement ratio of recycled coarse aggregate, respectively. Moreover, the residual shear toughness ratio increased almost linearly with increasing water–cement ratio, replacement ratio of recycled coarse aggregate, and volume content of steel fibers, and decreased with the increase of shear deformation, respectively. Finally, the formula for calculating the residual shear toughness ratio of SFRCAC was proposed by fitting the test results.

Introduction. The general corrosion model, made for reinforced concrete structures, must include the initiation of environmental influences such as carbonation, cracking and chloride ion penetration. It depends on the rate and degree of corrosion, corrosive effects in reduced areas, as well as the lower strength of bond between pre-stressed and unstressed reinforcement bars and concrete. The majority of earlier studies were focused on one-dimensional diffusion problems with an assumed constant corrosion rate.
 
 Materials and methods. In the aftermath of general corrosion, localized corrosion is accompanied by a release of hydrogen and alkaline water, chlorine ions. Crack propagation in reinforcement wires is calculated using the transient finite element software for chloride diffusion, which is time-dependent.
 
 Results. In most cases, the diffusion equation does not have a closed form solution, and therefore, the finite difference method can be used. The authors have shown that the corrosion rate decreases with time if current density has different water-cement ratios. If the water-cement ratio increases, the corrosion rate increases, as well.
 
 Conclusions. In a pre-stressed reinforced concrete beam, the corrosion of one bar affects the total corrosion of all bars and the reduction in the cross-sectional area of bars that does not exceed 15 %.

Diffusion characteristics and reinforcement effect of cement slurry on porous medium under dynamic water condition considering infiltration

Today, methods of determining the tensile strength of concrete are of considerable interest. These methods using the anisotropy of brittle materials and, in particular, concrete, with respect to compressive and tensile stresses, make it possible, based on the findings of the theory of elasticity, to determine the tensile strength when tested with a compressive load, which can be transferred to the sample much more easily than tensile forces. The results of tests of concrete by the method of compression of cylindrical samples and crushing of cube samples with hewn ribs between two round metal rods lying in the same plane closely match the tensile strength values obtained with direct tension. For all studied compositions, the value of the strength ratio increases as the water-cement ratio increases, both for concrete without additives and with additives of surfactants. Using additives of surface-active organic substances without changing the dependence of the strength ratio on the hardening time makes it smoother. It has been found that the fast decreasing value of the strength ratio, hardening period that corresponds to its minimum value, and further increase or stabilization of Rp / Rc depend on a number of factors of the cement used, storage conditions of surfactant additives, composition, etc. Under the influence of the different factors the position of the characteristic points on the curve of the strength ratio dependence on the hardening time can change and obey the general pattern. For concretes and mortars, the decrease in the strength ratios in the transition from 28 days to the age of 90 days makes up to 10–25% (and in some cases much more), which must be taken into account in appropriate cases when designing structures.

When geothermal fluid flows to the wellhead along the wellbore, there is a thermal transfer from the high-temperature geothermal fluid to the low-temperature formation. This process can directly lead to the decrease of wellhead temperature and loss of geothermal energy. Even though previous studies have confirmed that reducing the thermal conductivity of cement could validly cut down the heat loss of geothermal fluid, the influence factors of thermal conductivity are limited. In this research, we conducted detailed studies of the influence factors of thermal conductivity and compressive strength for cement. The results show that with the increase of water-cement ratio and thermal insulation materials, thermal conductivity and compressive strength decline. Furthermore, curing temperature is another important factor to improve the thermal preservation effect, but the testing temperature has the opposite influence. Based on these results, the present study concluded that porosity, Skeleton ingredients, curing temperature, and test temperature are vital factors for thermal conductivity. This research provides theoretical guidance for increasing the wellhead temperature of geothermal fluid and enhancing the efficiency of geothermal energy.