Increase Of Water-cement Ratio Research Articles

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

To reveal the chemical shrinkage (CS) characteristics of desulphurized electrolytic manganese residue (D-EMR) cement composite slurries, the CS was measured for slurries with different water-cement ratios (0.3 and 0.4) and varying D-EMR content (0 wt%, 5 wt%, 10 %, 15 wt%, 20 wt%, 25 wt%, and 30 wt%) using the expansion method. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and backscattered electron (BSE) image analysis were used to investigate the hydration products and pore porosity at different stages. In addition, the correlation between CS and hydration products was simulated using GEMS thermodynamics. The results indicate that as the water-cement ratio increases, the CS of D-EMR cement composite slurries increases significantly. At a water-cement ratio of 0.4, the CS decreases with increasing D-EMR replacement levels before 1829 h of hydration, but this trend reverses after 1829 h. At 8 days, the CS values for replacement levels of 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, and 30 wt% were 97.2 %, 94.9 %, 87.3 %, 84.4 %, 81.5 %, and 78.6 % of those of the pure cement pastes, respectively. The corresponding limiting chemical shrinkage values were 0.0712 mL/g, 0.0725 mL/g, 0.0742 mL/g, 0.0756 mL/g, 0.0769 mL/g, and 0.0780 mL/g. Finally, the prediction of long-term CS of D-EMR cement composite slurries is well described by both hyperbolic function prediction and thermodynamic simulations. These findings provide valuable theoretical support for the use of D-EMR as a supplementary cementitious material in construction.

An Experimental Investigation on Porosity and Permeability Co-efficent for Pervious Concrete Pavement by Statistical Modelling

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.

Comprehensive study on the penetration behavior of cement slurry under high-frequency pulsating pressure

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.

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

At the bottom of the geomembrane cut-off walls, pollutants may seep out through the bottom gap between the geosynthetic membrane and the low-permeability bedrock, contaminating the groundwater and the surrounding environment. Therefore, to address the occurrence of bottom gap seepage, this study adopts a mixture of attapulgite and cement in a certain proportion, mixed and stirred to form a sealing material. This sealing material is used to connect the bedrock and the geosynthetic membrane, thereby creating an efficient composite vertical barrier with special containment capacity. A series of laboratory experiments were conducted to investigate engineering properties of cement-attapulgite sealing slurry, including flow value tests, unconfined compressive strength (UCS) tests, improved flexible wall permeability tests, and bedrock and sealing slurry adhesion tests. The results show that the flow value of the slurry decreases with the increase of attapulgite content, and it increases with the increase of water-cement ratio. The UCS strength increases with the increase of attapulgite content, and it decreases with the increase of water-cement ratio, but the range of change is different. The hydraulic conductivity measured with hexavalent chromium solution as the penetrant is less than 50 % higher than that measured with water as the penetrant, and hexavalent chromium solution has little effect on the hydraulic conductivity of sealing slurry. The bonding performance between sealing slurry and bedrock is satisfactory, and the hydraulic conductivity of bedrock-sealing slurry is less than 1 × 10−7 cm/s (28d curing age), it is concluded that use of cement-attapulgite sealing slurry as bonding material between bedrock and geomembrane meets the engineering design requirements.

Experimental study on ultra-early tensile creep of cement paste

Tensile creep releases the internal tensile stress caused by the restriction of internal deformation in cement-based structure at ultra-early age (from initial setting to final setting) and thus reduces the risk of cracking under tension. However, the tensile creep measurement at that age is challenging due to insufficient strength of specimens. Therefore, a test device for measuring the tensile creep of ultra-early age cement paste was designed in this study, which applied multilevel incremental tensile load on the ultra-early age cement paste in a tailored molud. The effect of water-cement ratio and loading age on the ultra-early was studied using that device. The results revealed that the specific creep of ultra-early cement paste decreases exponentially with the increase of loading age, while increases with the increase of water-cement ratio. The ultra-early tensile creep of cement paste was characterized by variable viscosity dashpot element. Moreover, the increase rate of viscosity with time under external force was found equal to the creep modulus of cement paste, and in the logarithmic coordinate system, there is a linear relationship between the initial viscosity of cement paste and the loading age.

Study on Physical and Mechanical Properties of Micro-Cement Grouting Materials with Different Water-Cement Ratio

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

Rolled static cracking agent (RSCA) can solve the intractable problem of traditional bulk static cracking agent (BSCA) in engineering applications. This paper innovatively studies the rational water-cement ratio of BSCA and the immersion soaking time of RSCA under the condition of controlling temperature. Through the expansion and cracking performance experiments, the development characteristics of expansion pressure, the cracking effect of the single-hole specimen and the performance of hole spraying prevention under the action of BSCA and RSCA were compared and analyzed. The results show that: (1) The volume growth rate of static cracking agent decreases with the increase of water-cement ratio, and the fluidity increases with the increase of water-cement ratio. The rational water-cement ratio for BSCA application is 0.3, and the rational immersion time of RSCA is 2–2.5 min; (2) Under the bore diameters of 30, 35, 40 and 45 mm, the expansion pressure of BSCA with a water-cement ratio of 0.3 is 38.2, 52.3, 61.5 and 68 MPa, and the expansion pressure of RSCA immersed in water for 2.5 min is 43.5, 58.8, 69.5 and 75.1 MPa, respectively. Among them, the development speed of expansion pressure of BSCA is higher than that of RSCA, and the arrival time of the peak expansion pressure of RSCA is 1.7 times that of BSCA; (3) The crack initiation speed of single-hole specimen under the action of RSCA is 10.3 % lower than that under the action of BSCA, but the cracking speed of the former is 72.6 % higher than that of the latter; (4) The hole spraying occurs in BSCA under the bore diameter of 50, 55 and 60 mm, while the hole spraying occurs in RSCA under the bore diameter of 60 mm. In terms of bore diameter, the hole spraying prevention of the RSCA is better than that of BSCA. The research results enrich the static blasting technology and provide data support and theoretical reference for field application.

Evaluation method of shear toughness for steel fiber‐reinforced concrete containing recycled coarse aggregate

AbstractIn 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.

Research on Impact Factors of Workability of Roller Compacted Concrete Based on Modified Vebe Test

Abstract To obtain the optimum workability of roller compacted concrete (RCC), it is necessary to fully consider the degree of influence of each component of RCC. In this research, the influence of water-cement ratio, the content of cement slurry, the content of mortar, the sand ratio, the particle size of maximum aggregate, and the content of mineral powder on the workability of RCC was studied by modified Vebe test. The results showed that the Vebe consistency decreased with the increase of water-cement ratio. The recommended range of cement slurry surplus parameter was 1.1∼1.4; the recommended range of cement mortar surplus parameter was 1.2∼1.6; mixing the fly ash and silica fume into RCC is beneficial to its workability, but the content of fly ash could not exceed 20 %, and the optimum value of the content of silica fume was between 5 and 7.5 %; and the sand ratio has a significant effect on RCC, and there is an optimal sand ratio just like ordinary concrete, which is 34 % in this study.

The finite element model of chloride diffusion in pre-stressed corroded reinforcement bars of reinforced concrete structures

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

Grouting methods are known to effectively remediate the groundwater inrush in tunnels with weak water-rich sand layers. However, the diffusion characteristic of cement slurry flowing in rock and soil media with flowing water is one of the many critical issues that still remain unsolved. The cement-based grouting material diffusion characteristics of water in rock, considering four grouting parameters of water-cement ratio, water flow speed and fractal dimension of particle mass, were researched through a series of experiments such as cement particle filtration, nuclear magnetic resonance and diffusion test. Then compressive strength, scanning electron microscope(SEM) and mercury intrusion porosimetry(MIP) were performed on consolidated specimens to examine physico-chemical bonding mechanisms characteristics. The results indicate that 1) The viscosity of the effluent at the test point varies with the increase of water discharge velocity with different water cement ratio. When the water cement ratio is low, the viscosity of effluent increases first and then decreases with the increase of water flow rate. For high water cement ratio, the viscosity of the same test point decreases with the increase of water velocity. 2) The porosity of the consolidation with a low water velocity is lower than that of the media with a high water velocity within 4 m of the injection site. However, when it exceeds 4 m, the porosity has the opposite trend. 3) In the range of 0.3 ∼ 0.4 m, the grouting pressure at middle and low velocity is higher than that of high velocity. Beyond this range, the trend is reversed. 4) When cement slurry flows in particles, its pressure attenuation law is not affected by the state of dynamic water and is only related to the fractal dimension of particles. Its pressure attenuation decreases sharply with the increase of distance, when cement slurry flows in the particle mass with higher fractal dimension. Nevertheless, the flow pressure of cement slurry decreases slowly with the increase of distance at low fractal dimension. 5) The compressive strength of the consolidated body of cement and sand decreases with the increase of water-cement ratio and distance. Microstructural changes in sand fabric indicate that cement grouting material modified the porous network of consolidated sand. The pores were filled and particles were bonded by hydration product of cement.

Анализ методик испытаний гидротехнических бетонов на прочность

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.

Study on Thermal Conductivity of Thermal Insulation Cement in Geothermal Well

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.

Recycled Aggregate Pervious Concrete: Analysis of Influence of Water-Cement Ratio and Fly Ash under Single Action and Optimal Design of Mix Proportion

Pervious concrete is recommended, which is of great benefit to the ecological environment and human living environment. In this paper, the influences of five water-cement ratios and four fly ash contents to replace the cement by mass with a water-cement ratio of 0.30 on the properties of Recycled Aggregate Pervious Concrete (RAPC) were studied. Following this, based on the Grey relational-Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) optimization method, the strength, permeability, abrasion loss rate, and material costs of RAPC were adopted as evaluation indices to establish a mix proportion optimization model. The results show that the increase of water-cement ratio and fly ash replacement level of RAPC leads to decreased compressive strength while an increase in the permeability and abrasion loss rate. According to test results based on the optimal model 0.30 was identified as the best mix proportion. In addition, ecological-economic analysis of RAPC raw materials was carried out by comparing different natural aggregates. The results of EE (embodied energy) and ECO2e (embodied CO2 emission) pointed out that the combination of recycled aggregate and fly ash leads to significant ecological and economic benefits.

Laboratory Study on the Effect of Water-Cement Ratio on Strength Characteristics of Jet Grouting Columns

Jet grouting is one of the most widely applied soil improvement techniques. It is suitable for most geotechnical problems, including improving bearing capacity, decreasing settlement, forming seals, and stabilizing slopes. One of the difficulties faced by designers is determining the strength and geometry of elements created using this method. Jet grouted soil-cement columns in soil are a complicated issue because they are dependent on a number of parameters such as soil type, grout and water flow rate, rotation and lifting speed of monitor, nozzle jetting force, and water to cement ratio of slurry. This paper discusses the effect of the water-cement ratio on the physical and mechanical characteristics of soilcrete. In the laboratory, sandy soil mixed with cement grout with water-cement ratio varies from (0.7:1 to 1.4:1). To evaluate the characteristics of soilcrete, 96 specimens were prepared in the laboratory and tested at different curing times. The results indicate that the Uniaxial Compressive Strength (UCS) of soilcrete decreases with increasing the (W/C) ratio of the grout, where the soilcrete strength of W/C ratio of 0.7 is higher about 237% of W/C ratio of 1.4 at 28-day; the evolution of the (UCS) is proportional to the logarithm of the curing time; the ratio between the modulus of elasticity (Etg50) to the maximum UCS varies from 113 to 175; when the water-cement ratio increases, the dry density of soilcrete decreases, as a result, the (USC) of soilcrete decreases.

Improving latent heat storage capacity of polyethylene glycol/cement composite prepared via solution blending method

Adding phase change materials in building walls or roofs can help control the inner temperature of buildings. A kind of composite phase change material, sulphoaluminate cement-based polyethylene glycol (SPEG), can be prepared by blending polyethylene glycol (PEG)-water solution with sulphoaluminate cement. This study aims at improving the heat storage capacity of SPEG using five water-cement ratios (i.e., 0.2, 0.3, 0.4, 0.5 and 0.6). The microstructure, chemical composition, phase change characteristic, thermal and mechanical properties of the SPEGs were investigated, respectively. The results showed that with the increase of water-cement ratio, more hydration products were generated, and the precipitated PEG adhered to the surfaces of the hydration products. Although PEG did not change the hydration product types, it slowed the hydration process. When the water-cement ratio was 0.5, the heat enthalpy of SPEGs could reach up to 40.31 J/g. All the prepared SPEGs could keep their thermal stability under the temperature of 300 °C. After 200 thermal cycles the phase change enthalpy and temperature of SPEGs changed in a very small range. The thermal conductivity, compressive and flexural strength all increased with the increase of water-cement ratio, although the addition of PEG negatively affected the above indicators. The findings in this study are expected to help prepare cement-based phase change materials with high heat storage capacity.

Influence of deicing salt on the surface properties of concrete specimens after 20 years

The low temperature of ice and snow all year round in Sweden leads to the common use of deicing salt to melt the roads, but the splash of the deicing salt on the reinforced concrete (RC) on both sides of the roads brings about the deterioration of the durability of RC components. The chloride ions diffusion coefficient is an important parameter to evaluate the durability of RC. By adopting the rapid chloride migration method (RCM) and replacing chloride ions with iodide ions, the samples of concrete blocks exposed on the side of the highway for 20 years were taken. This is directly beneficial to study the influence of the type, content, and water-cement ratio of mineral additions on the diffusion and distribution of iodide ions in concrete and analyze the surface environmental effect depth of concrete. The influence of chloride ions on the pore structure and microscopic morphology of concrete also were studied by scanning electron microscope-energy dispersive spectrum and X-ray diffractometer. The results show that as the water-cement ratio increases, the surface environmental effect depth of concrete and the diffusion area of iodide ions gradually increase. Silica fume and ground granulated blast furnace slag (GGBF slag) have an impediment to the diffusion of iodide ions, especially with the high volume of the GGBF slag (about 50%), the diffusion of iodide ions is very low. In general, this research is helpful to provide some empirical ideas and suggestions for the manufacturing and durability design of concrete structures in marine environments or deicing salt road environments.

Experimental Study on Developing Mass Concrete Mixes as per Indian Standard 10262: 2019

In present study attempts to develop M15 grade mass concrete mixes using IS 10262:2019. The number of trial mixes were developed by maintain the cement content about 316 kg/m3 and Ground Granulated Blast Slag content (15%) for all the mixes. The water content and aggregates content was varied for all the mixes. The maximum size of coarse aggregates restricted to 40 mm. The fresh properties and hardened properties tests on mass concrete mixes were carried out as per IS codes. The results shows that mass concrete mixes can be developed by using IS 10262:2019 for given grade of concrete. The workability of mixes increases as water-cement ratio increases and also much provide better workability is achieved when cement is partial replaced with GGBS. The compressive strength for both cubes and cylinders and flexural strength values increases when partial replace 15% GGBS with cement. But the tensile strength value decreases when the partial replacement of GGBS with cement.

Three-dimensional reconstruction and sulfate ions transportation of interfacial transition zone in concrete under dry-wet cycles

The interface transition zone (ITZ) is widely recognized as the weakest phase in cement-based materials, and playing a critical role in the durability of concrete. The purpose of this paper is to investigate the performance difference and the diffusion of sulfate ions in cement matrix and ITZ under dry-wet cycles. Therefore, the three-dimensional structure of cement matrix and ITZ was reconstructed by CEMHYD3D and cellular automaton, which was used for exploring the formation and evolution law under the cycling conditions of corrosion. The unsteady diffusion equation of sulfate ions was established based on Fick’s second law and the impact factor ν of diffusion coefficient was introduced to analyze sulfate ions transportation. The simulation results were compared and discussed with the measured results. Results indicate that the porosity of ITZ is higher than cement matrix with the same water-cement ratio. Yet, the content difference of ettringite between cement matrix and ITZ hardly changed with the increase of water-cement ratio. The corrosion depth of sulfate ions in ITZ is approximately 2 mm deeper than cement matrix and the sulfate ions concentration in ITZ is greater than that of cement matrix at the same corrosion depth. Moreover, the diffusion rate of sulfate ions increases multiplying under dry-wet cycles and the increase of sodium sulfate concentration also accelerates the early corrosion rate. However, the influence of sodium sulfate concentration on the corrosion rate becomes insignificant as the water-cement ratio increases to 0.5. This study provides new insights in sulfate ions transportation about ITZ and cement matrix, the results of which are expected to provide a new direction for designing sulfate resistant concrete.

Pipe pressure of mining wet shot crete flowing in pipes

In order to explore the pressure change law of mining wet shotcrete in pipes, the rheological model was built based on rheology principle, and the computational formula of rheological parameters of wet shotcrete was deduced with the linear regression. 100 m full-scale pipeline platform of wet shotcrete was designed and built to study the relationship of pressure and other factors including flow rate, water cement ratio, mix proportion, and pipe bends. Results show: pipe pressure increases with the increase in flow rate and declines with the increase in water-cement ratio, the pressure may fluctuate with a high water cement ratio which can cause cement overhydration and bleeding separation. It will be more beneficial to transport materials if the continuous grading and straight pipe were considered. According to the tests of mix proportion 1:1.5:2.25, the pressure drop is 0.032 MPa·m−1 and the bend pressure drop is 1.3 times higher than in the straight line. We also conclude that solid phase pressure is bigger than liquid phase pressure and they both decline along the pipe based on FLUENT simulation. Finally, the formula of on-way resistance used in mine production was deduced.