Cement-sand Ratio Research Articles

Adhesive Strength of Modified Cement–Ash Mortars

The main aim of this article, carried out in relation to ash–cement mortars, is to determine the effect of complex additives of polyfunctional modifiers, including, in addition to superplasticizers, air-entraining and water-retaining additives, at different values of water–cement ratios. With the use of experimental–statistical models, the complex effect on the adhesive strength of cement–ash mortars of water–cement and ash–cement ratios, as well as complex additives of polyfunctional modifiers, including air-entraining and water-retaining additives, is considered. The extreme nature of the water–cement and ash–cement ratios on the adhesive strength of ash–cement mortars are established. Their optimal values are in the ranges of 0.7–0.75 and 0.35–0.4, respectively. The addition of a naphthalene-formaldehyde superplasticizer makes it possible to increase the adhesive strength of mortars by up to 40%. A positive effect is achieved along with the addition of a superplasticizer by introducing optimal amounts of air-entraining and water-retaining additives into the mortar mixtures. Quantitative parameters of mortar compositions that positively affect adhesive strength are established. The influence on the adhesive strength of the fly ash was also investigated, as well as on the binder–sand ratio. In addition, a positive effect on the adhesive strength of modified cement–ash mortars was experimentally shown by increasing the specific surface area of fly ash by regrinding it and increasing the cement–sand ratio.

Prediction of the Compressive Strength for Cement-Based Materials with Metakaolin Based on the Hybrid Machine Learning Method

Cement-based materials are widely used in construction engineering because of their excellent properties. With the continuous improvement of the functional requirements of building infrastructure, the performance requirements of cement-based materials are becoming higher and higher. As an important property of cement-based materials, compressive strength is of great significance to its research. In this study, a Random Forests (RF) and Firefly Algorithm (FA) hybrid machine learning model was proposed to predict the compressive strength of metakaolin cement-based materials. The database containing five input parameters (cement grade, water to binder ratio, cement-sand ratio, metakaolin to binder ratio, and superplasticizer) based on 361 samples was employed for the prediction. In this model, FA was used to optimize the hyperparameters, and RF was used to predict the compressive strength of metakaolin cement-based materials. The reliability of the hybrid model was verified by comparing the predicted and actual values of the dataset. The importance of five variables was also evaluated, and the results showed the cement grade has the greatest influence on the compressive strength of metakaolin cement-based materials, followed by the water-binder ratio.

A thermal conductivity prediction model of cement-based grouts for ground source heat pump

Cement-based material is frequently used in many aspects. For example, it is used as a sort of grout in a ground source heat pump system, whose heat conduction performance directly affects the heat change efficiency of the vertical ground heat exchanger. However, there are few thermal conductivity models applicable to cement-based grout materials, and the accuracy of published models needs to be improved. Therefore, a thermal conductivity prediction model for cement-based materials was performed according to the structure and heat conduction equation, which can predict the influence of many factors on thermal conductivity, such as aggregate content (sand-cement ratio), porosity and saturation degree. The overall accuracy is high, with 39 sets of data (75% of the data volume) whose errors are less than ±10%, meeting engineering applications, while the error using existing models mostly exceeds ±20%. This model can also predict a large proportioning range with the water-cement ratio from 0.3 to 0.7, the sand-cement ratio from 0.5 to 3.0, and the saturation degree from 0 to 1. Based on the model prediction results, the variation maps of different sand-cement ratios and porosity under dry and saturated conditions were proposed, and the simplified fitting formula for a range of common values was given.

Experimental Study of Multi-Angle Effects of Micron-Silica Fume on Micro-Pore Structure and Macroscopic Mechanical Properties of Rock-like Material Based on NMR and SEM

The experiment of rock-like material plays an important role in the simulation of engineering fractured rock mass. To further understand the influence of raw materials on rock-like materials, this paper carried out the indoor mechanical properties test and the micro-pore structure detection combining NMR and SEM. The effects of micron-silica fume (SF) on microporous structure parameters and macroscopic mechanical properties under different conditions of water–cement ratio (WCR) and sand–cement ratio (SCR) were discussed. The intrinsic relationship between parameters of different scales was analyzed. The experimental results showed that the porosity parameters of different radii gradually decreased with the increase in SF. The reduction rate of macroporous porosity was the greatest, and the decreasing rate of microporous porosity was the smallest. With the increase in SF, the microscopic characteristics of the internal surface changed from more pores, complex morphological distribution, rough surface to fewer pores, regular morphological distribution and flat and uniform surface. The box fractal dimension also showed a decreasing trend. Micro-pore structure makes a valuable contribution to the influence of SF on mechanical properties. The compressive strength and tensile strength increased with the increase in SF. The box fractal dimension and porosity of different radii were negatively correlated with mechanical strength. Different porosity parameters conformed to a good exponential relationship with mechanical properties. The research results can provide reference value and research space for subsequent rock-like material research.

Numerical Investigation of Triaxial Shear Behaviors of Cemented Sands with Different Sampling Conditions Using Discrete Element Method.

In cemented sand, the influences of the sampling factors (i.e., the curing time, cement–sand ratio, and initial void ratio) on the triaxial shear behavior were investigated using discrete element method. Cemented sand samples with different initial conditions were prepared and subjected to the consolidated drained triaxial shearing test. In the simulations, the peak strength, residual strength, and pre-peak stiffness of cemented sand were enhanced by increasing the curing time and cement–sand ratio, and the enhancements could be explained by the increases in bond strength and bond number. Resulting from the increases of these two sampling factors, bond breakage emerged at a greater axial strain but lower intensity. However, some uncommon phenomena were generated; that is, the contractive but strain-softening response occurred in the sample with a curing time of 3 days, and the shear band and the strain-hardening behavior coexisted in the sample with a cement–sand ratio of 1%. The peak strength and pre-peak stiffness were also enhanced by decreasing the initial void ratio, more distinctly than by increasing the curing time and cement–sand ratio. However, the residual strength, bond breakage, and failure pattern with the persistence of shear band were insensitive to this change.

Drying Shrinkage Properties and Initial Bonding Strength of 3D Printing Mortar

3D printing has emerged in the construction industry provide an effective and productive alternative construction methods. Cement-based material is the main choice in 3D printing construction due to its low cost and easy availability. This paper presents the drying shrinkage properties of hardened 3D printing mortar and the bonding strength of fresh mortar under the delayed phenomenon. Eight types of mortar mixtures in two series with varying percentages of sandy clay replacement ranging from 0% to 75% for both 1:1 and 1:2 cement sand ratios were used in the trial mix. Basic physical properties of 3D printing mortar such as workability, extrudability and buildability were conducted on the trial mix. Four mortar mixtures that complies with the basic 3D printing properties were used to conduct the drying shrinkage properties and the initial bonding strength test. The initial bonding strength test was conducted under delayed phenomenon for 0 minutes, 10 minutes, 20 minutes and 30 minutes. The experimental results showed a significant increase in drying shrinkage for mortars containing 75% sandy clay. However, the highest initial bonding strength is also achieved by mortars containing 75% sandy clay. The initial bonding strength of 3D printing mortar was decreased over the delaying time.

Influence of Layered Angle on Dynamic Characteristics of Backfill under Impact Loading

In order to explore the relationship between the filling surface angle and the dynamic characteristics of the filling body under impact load, this paper uses the Hopkinson pressure bar (SHPB) test system to study the influence of different filling surface angles, different cement–sand ratios and different strain rates on the dynamic peak strength, dynamic strength growth factor and failure mode of the filling body. The results show that with the increase in the average strain rate, the dynamic peak strength and dynamic strength growth factor of the layered filling body increase gradually. With the increase in the filling surface angle, the static and dynamic peak strength of the layered filling body decreases gradually, but there is no obvious change law linking the dynamic strength growth factor and filling surface angle. According to the failure mode analysis and the LS-DYNA numerical simulation results for the layered filling body, with the increase in the filling surface angle, the failure mode of the layered filling body changes from splitting failure under tension to shear failure. The research results in this paper can provide theoretical support for the stability of underground layered filling bodies.

Correlation Analysis between Microscopic Pore Parameters and Macroscopic Mechanical Properties of Rock-like Materials from the Perspective of Water-Cement Ratio and Sand-Cement Ratio.

To explore the effects of water-cement ratio and sand-cement ratio on micro-pore structure characteristics and macroscopic mechanical properties and thus improve the understanding of rock-like materials, the mechanical test and detection of micro-pore structure combining NMR and SEM were carried out. The effects of WCR and SCR on different porosity parameters and mechanical properties were discussed. The correlation and internal relationship between mechanical properties and parameters of different porosities and fractal dimensions were analyzed. Experimental results showed that the different porosity parameters and fractal dimensions increased with the increase in WCR. 1.0 (SCR) was the turning point of different porosity parameters and fractal dimensions. When the SCR was less than 1.0, the porosity parameters and fractal dimension gradually decreased, while when the SCR was greater than 1.0, the porosity parameters and fractal dimension gradually increased. Microscopic porosity parameters and fractal dimension played an important role in the influence of experimental factors on mechanical properties. Different porosity parameters and fractal dimensions were negatively correlated with mechanical properties. Compressive strength and different porosity parameters conformed to a good exponential relationship, while the fitting relationship between tensile strength and mechanical properties was not obvious. This study can provide a reference for the follow-up study of rock-like materials.

Effect of fly-ash as fine aggregate on the workability and mechanical properties of cemented paste backfill

An experimental study was conducted to investigate the effect of fly-ash(FA) as a fine aggregate on filling performance. The effect of FA content on the gradation distribution and compactness of the dry mixture is tested. Slump, bleeding rate, and unconfined compressive strength (UCS) of cemented waste rock-FA backfill (CWFB) samples were also tested at different FA content, solids content, and cement-sand ratio conditions. Results show that FA as a fine aggregate can effectively improve the mixture gradation performance. Short-term (3d/7d) strength increases with FA content, while long-term (28d) strength and slump first increase and then decrease, reaching a maximum value of 8.58 MPa and 27.4 cm respectively at 30% FA content. The bleeding rate first decreased and then stabilized (about 5.2%) with FA content. The UCS showed higher sensitivity to high solid content. The slump reduction rate of samples with high FA content decreases with solid content. Larger cement content will weaken the fluidity. When the cement-sand ratio increased from 1:6–1:4, the slump decreased from 27.5 cm to 23.5 cm, and the bleeding rate decreased to 4.05%. However, the mechanical properties are significantly improved with cement content. This study has positive implications for recycling the FA.

Effect of expanded polystyrene beads on the properties of foam concrete containing polypropylene fiber

In this study, foam concrete was produced using 3 different volumes of EPS beads (up to 100%), 3 different volumes of polypropylene(PP) fiber (up to 0.1)%, sand and 40% pre-produced foam which is fixed by volume. The water-cement ratio was 0.4 and the sand-cement ratio was chosen as 1. The foam concrete were cast into molds with a size of 100 x 100 x 500 mm and 150 x 150 x 150 mm prism. Unit weight, ultrasonic pulse, water absorption, splitting tensile strength, bending strength and compressive strength tests were achieved. Foam concrete were kept in laboratory standard conditions. According to the results of study, unit weight and ultrasonic pulse velocity vary between 970-1350 kg/m3 and 1.6-2.6 km/sec, respectively. The water absorption of the foam concrete decreased up to 65% as the EPS beads ratio increased. Since EPS beads do not contribute to the strength and act like a void, splitting tensile strength in specimens containing EPS beads decreased by up to 70%. The use of fiber contributes to the splitting tensile strength, especially in specimens that do not contain EPS beads, and it increased the strength by 78%. Similarly, the flexural strength of the PP fiber addition increased by up to 70%. As the EPS beads ratio increased, the flexural strengths decreased by 77%. With the addition of PP fiber, the compressive strength increased by 55%. However, since EPS beads' strength is negligible, it caused a 60% decrease in compressive strength.

Influence of Density, Porosity and Void Size on Thermal Conductivity of Green Lightweight Foamed Concrete

One of the methods to reduce the energy content of buildings is through selection of building materials. Strain on conventional energy can be reduced by employment of low energy materials and efficient structural design. The selection of materials also helps to capitalize on indoor comfort. For instant, the use of materials and components with small embodied energy or low thermal conductivity has enhanced the indoor comfort in building. Thus, a high level of insulation in any new material development is an essential step to an energy efficient design. The main purpose of this study is to investigate the thermal conductivity of green lightweight foamed concrete samples ranging from 650 until 1050 kg/m3 with constant cement-sand ratio of 1:1.5 and water-cement ratio of 0.5. This study was limited to the influence of density, porosity and void size on thermal conductivity of lightweight foamed concrete. Lower density foamed concrete translates to lower thermal conductivity. The density of foamed concrete is controlled by the porosity where lower density lightweight foamed concrete indicates greater porosity. Hence, thermal conductivity changes considerably with the porosity of lightweight foamed concrete because air is the poorest conductor compared to solid and liquid due to its molecular structure.

Experimental Study on the Properties of Phosphate-Based Materials for Rapid Repair of Concrete Cracks

This article studies rapid repair materials by mainly carrying out macro- and micro-performance impact tests. The static volumetric method was used to conduct pore volume-aperture analysis and prove the impact of the durability and repair performance of materials. The results show that 1) material impermeability can be effectively improved by increasing the ratio of active ingredients A:B and reducing the water-to-binder ratio. Adding an appropriate amount of fine aggregate can enable one to adjust the microstructure of the repair material, improve the compactness of the material, and effectively improve the impermeability. 2) An increase in the proportion of active ingredient A, water-binder ratio, sand-cement ratio and fly ash content will reduce the self-shrinkage of the specimen; with increasing NS and silica fume content, shrinkage increases. 3) Through analysis of pore size and pore volume, the total pore volume of the repair material is found to be reduced by 16.0% compared with cement mortar. Within a pore diameter range of 2.00–10.00 nm, the volume of the repair material increases by 78.9% compared to that for cement mortar. The total volume of the mesopores (2–50 nm) in the repair material accounts for 87.7% of the total volume, and the total volume of the mesopores in the cement mortar accounts for 81.23% of the total volume, which further illustrates the excellent macroscopic properties of the repair material.

Study on Energy Dissipation Characteristics and Damage Law of Backfill under Cyclic Impact

This research aims to study the damaging effect of underground blasting mining pillars on adjacent cemented filling bodies. The filling bodies were made by mixing ore rock with ash sand by the ratio of 1 : 4 and 1 : 6, respectively, which were subjected to cyclic impact tests with the split-Hopkinson pressure bar under the pressure of 0.2 MPa and 0.24 MPa to analyze the energy dissipation characteristics and damage law. The results showed that as the stress wave induced by the cyclic impact was transmitted to the composite specimen, the energy was absorbed for crack growth and development. Then, the energy reflection ratio increased while the energy dissipation ratio and transmission ratio decreased. For the combined specimen with the cement-sand ratio of 1 : 4, after five cycles of impact under the condition of Ip = 0.2 MPa, the damage variables were 0.07, 0.11, 0.51, and 0.56, respectively, since the second time; under the condition of Ip = 0.24 MPa, the damage variables were 0.17, 0.29, 0.55, and 0.66, respectively. After reaching the damage threshold of 0.63, the damage variable showed nonlinearity. Moreover, it was found that the mechanical properties of the filling body affect the whole combined specimen, and the dynamic strength of the combined specimen with the cement-sand ratio of 1 : 4 was higher than that of the cement-sand ratio of 1 : 6. Therefore, it can be concluded that during the two-step pillar recovery, the amount of blasting explosive can be appropriately reduced, and the number of blasting can be increased to reduce the damaging effect of blasting impact on the cemented pillar and reserved pillar to maintain stability.

Experimental Study on Strength and Permeability Characteristics of Cemented Rock-Tailings Backfill

To study the strength and permeability characteristics of cemented tailings backfill with different cement–sand ratios and different waste rock contents, uniaxial compression strength test and permeability test were carried out respectively. The porosity of cemented tailings backfills after solidification was observed by scanning electron microscope. The effects of cement–sand ratio and waste rock content on the internal porosity and overall permeability of cemented tailings backfill were studied. The test results showed that the cement–sand ratio and waste rock content have certain effects on the strength and permeability of the backfill body. When the cement–sand ratio was fixed, the uniaxial compressive strength and permeability of the backfill body increased first and then decreased with the increase of waste rock content. When the waste rock content was 10%, the uniaxial compressive strength of the backfill body reached the maximum, and when the waste rock content was 30%, the permeability reached the maximum. Due to the increase of the area of waste rock particles in the cross-section, the area of gas passing rapidly decreased, resulting in the decrease of the permeability growth rate. When the waste stone content was fixed, with the decrease of cement–sand ratio, due to the decrease of cementitious materials, more micro-cracks were produced in the curing process of backfill body, resulting in the decrease of uniaxial compressive strength and the increase of permeability.

Experimental and Analytical Investigation into the Synergistic Mechanism and Failure Characteristics of the Backfill-Red Sandstone Combination

The stability of underground goaf in filling mining is dominated by the interaction mechanism of the backfill-surrounding rock combination. In order to investigate the interaction mechanism and failure characteristics of the backfill-surrounding rock combination, backfill-red sandstone combinations with three different cement–sand ratios were prepared for uniaxial compression tests. The deformation and failure characteristics of the specimens were analyzed. It was found that at the cement–sand ratio of 1:4, the backfill and red sandstone interacted with and restricted each other, and the through cracks appeared in the whole specimens, which indicated that the backfill and red sandstone can jointly resist external loads and play a role in common bearing. However, with the decrease of the cement–sand ratio, the stress mainly acts on the backfill, and the deformation observed in the backfill is large while there is no obvious rupture in the rock. Based on the failure characteristics and the stress–strain curves of the specimens, the damage constitutive relationship that can describe the failure process and deformation characteristics is proposed. Correlated with the experiment results, the damage constitutive equation is established in three stages including compaction pre-synergy stage, quasi-elastic synergy deformation stage and rupture deformation stage. The failure characteristics observed in each stage are analyzed. The research results are of great significance to accurately understanding the interaction between backfill and surrounding rock, which can be used to design and select the mixture ratio of the filling materials.

Strength investigation of the cemented paste backfill in alpine regions using lab experiments and machine learning

Cemented paste backfill (CPB) is increasingly used in mines in alpine areas. The strength of CPB is unstable due to the influence of multiple factors such as low temperature. In order to obtain the uniaxial compressive strength (UCS) of CPB under the action of different factors, a large number of laboratory tests had to be conducted in the past, which is time-consuming and laborious. In this paper, a research on the UCS is conducted by means of a combination of indoor tests and machine learning. The sparrow search algorithm is used to optimize the extreme learning machine, thus solving the uncertainty of the extreme learning machine in determining the initial weights and thresholds. The strength prediction model of CPB based on SSA-ELM model is constructed with the curing temperature, sand-cement ratio, slurry concentration and curing time as input variables and UCS as output variables. Compared with the original ELM, the PSO-ELM and BP-ANN, the correlation coefficients improved from 0.8817, 0.9511, 0.9187 to 0.9979, which indicates that the SSA-ELM model has better prediction accuracy. In addition, correlation analysis shows that the low temperature(<20 °C) environment has the largest effect on the UCS, which affects the development of UCS by influencing the process of hydration reaction.

Effects of Soil-Cement Stabilization on the Index Properties of Subgrades of Three Selected Roads in the Niger Delta Region of Nigeria

In this study, the impact of soil-cement stabilization on the index properties of the subgrade of roads was investigated. Efforts were on the means of improving the bearing capacity of the subgrade of a flexible pavement structure. Three selected roads (Ogbia-Nembe, section of the East-West Road and section of Port Harcourt-Aba Road) in the Niger Delta Region of Nigeria were examined to determine the effect of sand-cement stabilization on the compaction index property of their undisturbed subgrade and the optimal ratio of soil-cement on the expansive soils at which the California Bearing Ratio (CBR) is optimized. Disturbed soil samples were collected from twenty trial pits on each of the three study roads using a hand ulger and tested for their respective compaction index properties. It was discovered that their California Bearing Ratio (CBR) was very low. Some of the collected specimen materials were stabilized with varying percentages of soil-cement contents ranging from 6% - 14% in order to ascertain its effects on the compaction index properties of the sample soils. Results of the various stabilization test procedures show that: Stabilization of the soil using Soil-Cement Stabilization affected the Compaction Index properties of the soil and further improved the California Bearing Ratio (CBR). On the Ogbia-Nembe Road; Soil-Cement stabilization improved the CBR and is optimized at a 10% sand-cement ratio with optimum moisture content ranging from 6.2% - 14%, maximum dry density ranges from 1700 - 1780 kg/m3, yielding an average CBR of 42.7% for soaked samples. On the section of East-West Road from Eleme Junction to Etteh Junction; Soil-Cement stabilization improved the CBR and is optimized at a 14% sand-cement ratio with optimum moisture content ranging from 6.2% - 14.2%, maximum dry density ranges from 1660 - 1800 kg/m3, yielding an average CBR of 43.9% for soaked samples. On the section of Port Harcourt-Aba Express Road from Eleme Junction to Osisioma Junction; Soil-Cement stabilization improved the CBR and is optimized at a 12% sand-cement ratio having an optimum moisture content ranging from 5.4% - 17.3%, maximum dry density ranges from 1610 - 1740 kg/m3, and an average California Bearing Ratio for soaked samples at 40%.

Synthesis of Sustainable Ternary Binders and Sand-Cement Ratio on the Mechanical and Microstructural Properties of Geopolymer Foamed Concrete

Synthesis of Sustainable Ternary Binders and Sand-Cement Ratio on the Mechanical and Microstructural Properties of Geopolymer Foamed Concrete

The Effect of Using Plastic Strips and Sheets on the Properties of Slurry Infiltrated Fiber Concrete

Slurry Infiltrated Fiber Concrete (SIFCON) is a high-strong material that is regarded as a unique type of high fiber content concrete. This paper aims to study the influence of the use of plastic strips and plastic sheets in the SIFCON slurry. Three sets (normal SIFCON as control, SIFCON with plastic strips, and SIFCON with plastic sheet), in a 1:1.08 cement-sand ratio by weight has been used with water to cement ratio (w/c) by weight equal to 0.3, and superplasticizer equal to 1% by weight. In addition, 6% by volume crimped steel fibers with an aspect ratio of 60 were applied and 1.34% by volume plastic was used, in strips of 5×1cm for both prism and cube samples and in sheets of 25×5cm and 7×7cm for prism and cube samples respectively. The compressive and flexural strength tests studies were conducted on typical cubes of 10×10×10cm and prisms of 40×7×7cm respectively to find out the way the plastic affects the SIFCON properties. The results indicate that the models with plastic sheets placed in SIFCON slurry give the highest compressive and flexural strength whereas the models with plastic strips gave the lowest. The difference percentages in compressive and flexural strength were -27.3, 8, -3.8 and 66.6% for all sets respectively when compared to the control set (using no plastic).

Experimental study on acoustic emission characteristics of cemented rock-tailings backfill

Cemented tailings backfill is an important development tendency of mine filling. Aiming at the cemented rock-tailings backfill material, the experimental tests on the acoustic emission characteristic of the backfill body under uniaxial compression was carried out, in which different cement-sand ratios (1:4, 1:6, 1:8, respectively) and waste rock contents (0%, 10%, 20%, 30%, 40%, respectively) were adopted. Through characteristics analysis of AE ringing count, cumulative hits and r value, the strength and deformation characteristics of the backfill body were obtained, and the influence mechanism of cement-sand ratio and waste rock content on the mechanical properties of the backfill body was revealed. The results indicated that as the waste rock content increased, the primary pores of the backfill body increased, the elasticity of backfill reduced, the plasticity of backfill increased, the uniaxial compression strength of the backfill body firstly increased and then decreased, the residual strength in the post-failure stage of backfill increased. Through analysis of microstructure by SEM and XRD tests, it was found that the most hydration products of the backfill body were C-S-H, followed by AFt and Ca (OH) 2, while the C-S-H was the main source of the cement-based materials strength.