Cement Mortar Blocks Research Articles

The Incorporation of Spent Coffee Grounds as an Additive in Cement Ventilation Blocks

Introduction The growing coffee industry has created a lot of waste in the form of spent coffee grounds (SCG), mainly disposed of through landfills. Recycling them into concrete construction products helps reduce their carbon effect on the atmosphere. According to earlier investigations, the SCGs have potential usage as supplemental construction materials across various civil engineering applications. However, the absence of thorough research and successful practical implementations in the sector necessitate further detailed studies in ventilation block application. Aims This study investigates the workability, compressive strength, water absorption and thermal performance of cement mortar containing different percentages of SCG in ventilation block production. Methods Cement, sand, and water with the 1: 2.75: 0.6 ratio and different percentages of SCG are used in the mortar mix as additives. The specimens were cast in cubes (50 mm x 50 mm x 50 mm) to investigate the workability, strength, water absorption and dry density. Further, the ideal mix was chosen to produce ventilation blocks. The prototype cubicles made from the SCG ventilation blocks were used for continuous indoor temperature monitoring. Results The results show that adding high amounts of SCGs into mortar has decreased workability and compressive strength in cement mortar blocks. However, the water absorption has reduced with the increased percentage of SCG added to the mix. Based on the results, the SCG0.75 is the most suitable ratio to be used as it showed a flowability of 48%, a compressive strength of 12.574 MPa and water absorption of 6.107%, which is ideal for producing the ventilation block. In addition, the temperature monitoring results showed a reduction in the indoor temperature that used the SCG ventilation block. Conclusion This result suggests incorporating SCG in the ventilation block requires a suitable percentage of the SCG to fulfill the workability and strength of the block. Nevertheless, it may reduce indoor temperature, thus providing better thermal comfort. This study enables the SCG waste products to be used as sustainable materials in ventilation block production.

Medium transmission property of the interfacial transition zone between MK-GGBFS geopolymer mortar and aggregate

In this study, metakaolin (MK)–ground granulated blast furnace slag (GGBFS) was used to prepare geopolymer mortar, and concrete was prepared using prismatic-shaped basalt or aged cement mortar block as coarse aggregate. The pore structure characterization of the mortar, chloride binding capacity of the corresponding paste and the micro dimension of the interfacial transition zone (ITZ) in concrete were analysed by using a mercury intrusion porosimeter, the chloride adsorption equilibrium method and scanning electron microscopy-energy dispersive spectroscopy, respectively. The medium transmission properties of the concrete and corresponding mortar were analysed through a moisture diffusion test, chloride migration test, and chloride natural diffusion test. On this basis, the permeability resistance of the ITZ in geopolymer concrete was studied by manipulating the parameters for the basalt aggregate. The result shows that the geopolymer mortar exhibits higher porosity compared to cement mortar with similar strength, while the most probable pore size is significantly smaller, with more than 80% of the pores showing a pore size of less than 50 nm. The chloride binding mechanism for geopolymer paste primarily involves physical adsorption, and shows a greater binding capacity than cement paste at a chloride ion concentration greater than 1 mol/L. The medium transmission coefficient for geopolymer concrete is found to be 55.1–79.0% of that of cement concrete for the same parameters of the coarse aggregate. The impermeability of geopolymer concrete and its ITZ is found to be always better than that of cement concrete for varying parameters of the coarse aggregate.

Experimental and numerical investigation on the peak value and loading rate of borehole wall pressure in decoupled charge blasting

Decoupled charge structures are widely used in contour blasting because of their lower peak value and loading rate of the borehole wall pressure (BWP), which plays an important role in the contour blasting effect. The filling medium and decoupling ratio are the two key factors of decoupled charge blasting, and their effects on the peak value, rise time and loading rate of BWP need to be investigated. In the present study, physical model tests of decoupled charge blasting on cement mortar blocks (400 × 400 × 200 mm) were conducted under different filling mediums and decoupling ratios, and polyvinylidene fluoride (PVDF) gauges were used to directly measure the BWP. In addition, a numerical model was developed and verified to simulate the same decoupled charge blasting tests and some other tests with additional decoupling ratios. The measured and simulated results both showed that the peak value and the loading rate decreased with increasing decoupling ratio. Compared with the theoretical formulas, the modified power function formulas provide more accurate peak values. The peak pressure, rise time and loading rate were higher in water-coupled blasting, and the ratio of the peak pressure in water-coupled blasting to that in air-coupled blasting was between 2.35 and 4.28 under decoupling ratios of 2∼5. When the peak pressure was the same, the loading rate in the water coupling blasting was always lower than that in the air coupling blasting.

Experimental study of the dynamic responses of surrounding jointed rock masses and adjacent underground openings and induced ground vibrations subjected to underground explosion

The shock wave generated after underground blasting might lead to severe catastrophe or irreparable destruction of adjoining underground and ground structures. To investigate the dynamic response of rock masses and adjacent underground openings and induced ground vibrations subjected to underground blasting, a sequence of laboratory tests was implemented with explosive charges and cement mortar blocks. The results show that not only the charge loading density but also the joint orientation affect the ground peak particle velocity (PPV) in a significant way, as well as the first peak strain at the neighbouring opening and in the surrounding rock masses. The first peak strain of the rock masses has a rising tendency with increasing charge loading density or decreasing scaled distance. The PPV on the ground clearly increases with increasing charge loading density. The first peak strain of the rock masses and ground PPV are dominated by the wave path, which is determined by the relative locations of the explosion source, measuring point and joints. The principal frequency of ground vibrations shows an increasing trend with increasing joint orientation, while the charge loading density slightly impacts the principal frequency. These research findings could enhance the comprehension of blasting wave propagation through jointed rock masses and contribute to the stability evaluation of aboveground and underground structures subjected to underground explosions.

Effect of nano-MgO on basic properties and microstructures of cement-based materials

Nano-magnesium oxide (MgO) can be used as an expansion agent for cement-based materials, but little is known about the influence of nano-magnesium oxide on the mechanics, microstructure and expansion stability of cement materials. The influence of nano-magnesium oxide on the consistency, fluidity, porosity, dry and wet densities, mechanical properties and microstructures of cement-based materials was researched in this study. The results show that the compressive strength and flexural strength of the cement mortar test block containing nano-magnesium oxide particles increase and are higher than those of the control cement mortar test block at any time. The addition of nano-magnesium oxide increases the mechanical strength of the cement mortar block, and the strengthening effects are most obvious in the early stage of maintenance. When the curing age is 28 days and the nano-magnesium oxide content is 1.5%, the compressive strength and flexural strength of the modified cement mortar test block are the best. Fourier transform infrared spectroscopy and scanning electron microscopy show that the expansion effect of nano-magnesium oxide makes the microstructure of cement-based materials denser and more uniform. This paper also discusses the influence mechanism of nano-magnesium oxide on cement-based materials, which provides a reference for the application of nano-magnesium oxide in cement-based materials.

Preparation and application of high-performance composite polymer emulsion cement waterproof coatings

PurposeThe purpose of this paper is to develop a high-performance composite emulsion cement waterproof coating. The coating has excellent durability and is effective in protecting cement mortar substrates from harmful ions.Design/methodology/approachThe polymer cement waterproof coatings with different emulsion compounding ratios were tested for mechanical properties and water resistance after alkali immersion, water immersion, thermal aging and UV aging, and the coatings were analyzed by infrared spectroscopy after aging to evaluate its durability. Meanwhile, the coating that presents favorable durability was applied to cement mortar test blocks. The protective effect of the coating on the test blocks was tested by immersion method, and X-ray diffraction analysis was performed on the eroded test blocks.FindingsThe coating with neoprene latex/acrylate latex weight ratio of 90/10 presents favorable durability and has superior overall performance. Besides, when it is applied to cement mortar blocks, the coatings effectively reduced the erosive effect of harmful ions on cement mortar blocks, resulting in much lower mass change ratios and less internal structural damage of the blocks significantly.Originality/valueThe obtained coating will be of great application potential for use in building waterproofing construction. Moreover, the coating can practically prevent chloride ions and sulfate ions from penetrating cement-based materials.

Grinding kinetics of lead–zinc tailing powders and its optimal particle size as a pozzolanic admixture in cement mortar

Recycling lead–zinc tailing powders (LZTPs) as pozzolanic admixtures can effectively solve its stockpiling and hazards problems synchronously, and mechanical grinding can increase the recycling utilization quantity and efficiency of LZTPs. Based on the laser particle size distribution (PSD) and activity index test results, the grinding kinetics, Rosin-Rammler-Bennet (RRB), Swebrec distribution model, and fractal theory of LZTPs have been studied. The results show that the grinding process of LZTPs is described quantitatively in the Divas-Alyaviden grinding kinetics equation, and the grinding efficiency of LZTPs becomes negligible after grinding for 120 min. Moreover, the PSD of LZTPs was remarkably consistent with the RRB, Swebrec distribution model, and fractal theory. The activity index increases with the grinding time. The gray correlational analysis revealed that a particle size range of 3.3 ∼ 6.5 μm presented a maximal positive effect on the activity index. In addition, the leaching toxicity of Pb, Cr, and Cd of LZTPs cement mortar block is below the standard limit of TCLP 1211 and it is safe to use the mortar with the addition of 30% LZTPs. The optimal grinding time for LZTPs was 90 min taking into account the economic and technical benefits.

Investigation on the Shear Behavior of Rough Rock Joints Prepared by Three-Dimensional Engraving Technique

Abstract Laboratory shear test is an important and widely used method to investigate the shear behavior of rock joints, and the preparation of joint specimens is a key factor that influences test results. In order to study the shear mechanism of rough rock joints with different morphologies in the laboratory, an innovative three-dimensional (3D) engraving technique was employed to produce specimens with rough joints. Intact sandstone and cement mortar blocks were used as model materials. The engraving parameters were determined to ensure a satisfactory engraving precision and to save as much time as possible for an engraving process. Three Barton profiles with joint roughness coefficient (JRC) values of 2.8, 10.8, and 18.7 were selected as the morphology prototypes for automatically engraving the model material blocks to obtain rough joint specimens. Shear tests were then conducted under four normal stress levels in the laboratory. In addition, numerical simulations on joints with the same physico-mechanical properties, surface morphology, and boundary conditions as the joint tested in the laboratory were performed. The failure characteristics, shear behavior curves, and shear strength obtained from numerical and experimental studies were analyzed considering the effect of joint materials, joint roughness, and applied normal stress. The shear mechanism of rough joints was investigated, and the analysis indicated that the results of shear tests by simulation and experiment were similar. The results revealed that it is feasible to make rough joints by engraving either real rocks or commonly used model materials (e.g., cement mortar).

Bacillus Subtilis as Self-Healing Agent in Cement Mortar: The Effect of Curing Time and Amount of Calcium Lactate on Strength

Crack growth is a major cause of failure in structures that are made using cement and concrete. Healing of these cracks can increase the life span of structures. In the present study micro-organism based self-healing of structures is studied. A commonly occurring micro-organism bacterium called Bacillus Subtilis, is used in the manufacturing of cement mortar blocks as a self-healing agent for cement mortar blocks, with the use of Calcium Lactate as feed for bacteria. In the first step, colonies of Bacillus Subtilis were grown and added with calcium lactate to produce a solution. The solution was then kept for one week to observe the metabolic product of Bacillus Subtilis. It was found that the bacterial product was composed of CaCO3 and thus the bacteria is suitable to be used as self-healing agent. Self-healing cement mortar blocks were made by adding Bacteria and Calcium Lactate with usual ingredients of cement mortar, i.e. cement, sand and water. It was found that the bacteria were also effective in converting Calcium Lactate to Calcium Carbonate, when mixed in cement mortar blocks. It was observed that the pores of cement mortar blocks were filled by Calcium Carbonate and that cracks get healed by the deposition of Calcium Carbonate in the cracks. Cement mortar blocks, with and without healing agent, were made to compare the effect of curing time. The samples were tested after seven, fourteen and twenty-eight days to compare the effect of healing agent. All the samples with the healing agent showed a higher compressive strength in comparison with the samples that were made without healing agent. Different percentages of Calcium Lactate, ranging from 1-7% were also used to find the best composition for future use. It was found that the compressive strength was increasing up to 5% while above 5% the increase was marginal thus it is proposed that Calcium Lactate should be used in between 5-7 % to reduce the cost of self-healing cement in construction industry.

Experimental and numerical study on the effect of water-decoupling charge structure on the attenuation of blasting stress

The blasting fracturing technique is one of the most promising options for enhancing the permeability of reservoir rock masses in the exploitation of petroleum, coal, uranium and other deep resources. The increase in permeability strongly depends on the shock wave acting on the reservoir rock mass to create a fracture network surrounding the blasthole, which is significantly affected by the decoupling coefficient of the charge. This paper studies the effect of the water-decoupling charge structure on the distribution of blasting stress, as well as the morphology of blasting-inducing fractures. In this work, physical model experiments of water pressure blasting on cement mortar blocks (3.1 m × 3.1 m × 1.0 m) are first conducted to study the attenuation law of explosive stress along the radial direction under the condition of four different water-decoupling coefficients of the charge (i.e., 1.0, 1.79, 2.57 and 3.29). In addition, a square numerical model with one circular blasthole is modeled with a particle assembly based on the discrete element method to simulate the same water pressure blasting tests as those performed in the physical model experiments. The results from the physical model tests and numerical simulations both show that the attenuation amplitude of the peak value of the explosive stress wave along the radial direction first decreases and then increases as the water-decoupling coefficient of the charge increases. In particular, the numerical results also reveal that the distribution range of the fracture network is strongly related to the attenuation of the blasting stress. In comparison with the other three water-decoupling coefficients tested in this paper, 2.57 proves to be the best coefficients for inducing the most extensive fissure distribution from the blasthole. Thus, in water pressure blasting, be an optimal decoupling coefficient for receiving the best blasting effect must exist, and selecting an appropriate water-decoupling coefficient for blasting is beneficial for enhancing reservoir permeability.

Experimental Study on Shear Behavior of Bolted Cement Mortar Blocks under Constant Normal Stiffness

In this paper, the influence of bolting on shear mechanical behavior of cement mortar specimens were studied. First, a shear test apparatus which could provide CNS (constant normal stiffness) condition was designed. Then, more than 140 bolted and non-bolted cement mortar blocks (100 × 100 × 100 mm) were prepared. The strengthening effect of bolts with diameters of 0 – 10 mm on cement mortar specimens was studied under different initial normal loads ranging from 20 kN to 60 kN and constant normal stiffness of 420 kN/mm. Two simplified models of shear behavior of reinforced cement mortar blocks were proposed. The most important influence of bolt on the cement mortar blocks was to strengthen the post-peak shear strength rather than the peak shear strength, and the strengthening effect was reduced under high initial normal force. The cohesion of cement mortar blocks was reduced while internal friction angle was increased in residual sliding stage by bolts. The dilation of reinforced cement mortar specimens in post-peak shear stage was significantly reduced due to bolting, and the larger the bolt diameter, the greater the reduction in the block dilation.

Modification and in-place mechanical characteristics research on cement mortar with fly ash and lime compound admixture in high chlorine environment

As industrial waste, the comprehensive utilization of fly ash involves many fields, among which it is widely used in cement mortar and concrete. As brine water is used in the preparation of filling slurry of Sanshandao Gold Mine, the chloride ions in the slurry have a great negative effect on the strength of the backfill. Therefore, the effects of fly ash and lime on the transport performance and the mechanical properties of cement mortar test blocks were studied by experiment. Based on fly ash XRD analysis, cement mortar block scanning electron microscope test (SEM) and fly ash with various amount and different way of adding test, the mechanism of improving the strength of the cement mortar test block produced by the fly ash and the best mixing amount of the fly ash were determined under the condition of brine water through experiment and theoretical research. Application of fly ash in undersea metal mine is a major breakthrough in the application of filling materials of metal mine undersea metal filling, having great effect on reducing the adverse effects on the strength of the filling body of bittern ions and improving the strength of the filling body.

Comparative study on mechanical characteristics of precast HMA block versus concrete block

ABSTRACTWhile precast cement mortar block has often been used in modular pavement, precast HMA (Hot Mix Asphalt) block has the advantages of flexible behaviour, no curing and recycling, etc. In this project, the mechanical characteristics of the precast HMA block were evaluated by comparing with precast cement mortar block. The objective of this project was to develop a method for the design of precast HMA block and the evaluation of its mechanical characteristics. The research contents include proportion design and preparation of precast HMA block, mechanical test of precast HMA block, comparative analysis between precast HMA block and precast cement mortar block. Through analysis on the mechanical characteristics of precast HMA block with non-reinforced and reinforced, the research results have indicated that the bending strength of precast HMA block decreases gradually with the increase of aggregate diameter. The comparative results have further indicated that the bending strength of precast HMA block can match the strength of the precast cement mortar block and that it can be applied in modular asphalt pavement. The precast HMA block has provided a feasible technology in modular pavement option.

Effects of the Notch Angle, Notch Length and Injection Rate on Hydraulic Fracturing under True Triaxial Stress: An Experimental Study

This study focused on the effects of the notch angle, notch length, and injection rate on hydraulic fracturing. True triaxial hydraulic fracturing experiments were conducted with 300 × 300 × 300 mm cement mortar blocks. The test results showed that the fracture initiation pressure decreased as the notch length and injection rate increased, whereas, the fracture initiation pressure decreased as the notch angle decreased. Furthermore, the direction of the hydraulic fracture was always along the direction of the maximum principle stress.

Experimental and statistical study on the irregularity of carbonation depth of cement mortar under supercritical condition

The heterogeneity of a cement-based material results in a random spatial distribution of carbonation depth. Currently, there is a lack of both experimental and numerical investigations aiming at a statistical understanding of this important phenomenon. This paper presents both experimental and numerical supercritical carbonation test results of cement mortar blocks. The carbonation depths are measured along the carbonation boundary by the proposed rapid image processing technique, which are then statistically studied by calculating, e.g., their probability density and power spectral density (PSD). The results indicate that the distribution of the carbonation depth can be approximately represented by a lognormal distribution function and the PSD has quantitative correlation with some of the statistic parameters used in the simulations. In particular, the effects of the autocorrelation lengths and the coefficient of variation of porosity, which are used to define the random porosity field, on the irregularity of carbonation depth are analyzed numerically in details and validated by experimental results. The study has shown that using a random field of porosity with due consideration of spatial correlation and variance, the irregularity of carbonation depth can be realistically captured by the numerical model. The numerical results confirm that lognormal distributions represent the random nature of carbonation depth well and the average and variance of the irregular carbonation depth increase with the increase of carbonation time, autocorrelation length and coefficient of variation of porosity. The study also offers a potential method to numerically calibrate some of the statistic parameters required by a numerical carbonation model through comparing the PSD with that from experimental tests. Overall the methodology adopted in the paper can provide a foundation for future investigations on probability analysis of carbonation depth and other similar work based on multi-scale and -physics modelling.

The influence of excavation damaged zone on the mechanical and thermal behavior of cement mortar block around an opening

To investigate the influence of Excavation Damaged Zone (EDZ) on the mechanical and thermal behavior, EDZ was artificially generated around an existing circular hole in a mortar specimen. By applying high compressive stresses on the boundaries of a specimen and repeating loading and unloading cycles, EDZ was generated around the hole. An engineering heater was installed at the hole and the temperature of the heater was maintained at 75°C during the tests. Tangential strains and temperature were monitored at several points around the hole and compared to those measured in the specimen without EDZ. For elliptical and circular damaged zones, the tangential strain in the EDZ increased by as much as 88% and 58%, respectively and temperature in the EDZ decreased by 2.8°C and 0.85°C, respectively. Two-dimensional thermal-mechanical coupled numerical simulation using Particle Flow Code 2D (PFC2D) was carried out to analyze and to demonstrate the experimental results. For the numerical simulation, thermal parameters were determined using the results obtained from sensitivity analyses by a factorial design method. The TM-coupled PFC2D modeling results indicated that significant changes in mechanical and thermal behavior were observed, when the elliptical and circular EDZ was considered. And that the laboratory test results were successfully reproduced.

Evaluating changes in fundamental cross-sectional mode of vibrations using a modified time domain for impact echo data

The impact echo (IE) method is a truly non-destructive test and can be very useful for structural health monitoring of concrete structures. Results from the present study provide an improved understanding the data from this method. Experiments were carried out using a cement mortar block which was subjected to uniform compression and the changes in the IE response in terms of the fundamental frequency of cross-sectional mode of vibrations were studied at different levels of applied load. A combination of the continuous wavelet transform (CWT) and fast Fourier transform (FFT) was used to study changes in the fundamental frequency. The results obtained from the modified method are compared with the results obtained from the traditional analysis, where only the FFT is applied using the entire waveform. It is found that the former has a clear potential of being more useful for a better understanding of the peak load that a structural element has been subjected to (in the past) compared to the latter. From the limited experiments carried out, it was found that in the former case, a change in the dominant frequency was observed at a much lower level of applied load (about 30% of failure) whereas in the latter such changes were seen at a much higher (about 70–80% of failure) load level.

Mechanism of anomalous low friction phenomenon in deep block rock mass

Deep rock mass has the unique “self-stressed” block-hierarchical structure, anomalous low friction (ALF) was one of the typical nonlinear geo-mechanical and dynamic responses in deep block rock mass, which occurred as the result of movements of large-scale geo-blocks under the impact of external pulses (such as a deep confined explosion, earthquakes, rock bursts and etc.). ALF phenomenon obtained its name to describe the curious phenomenon that the friction between interacting geo-blocks quasi-periodically disappears at some discrete points in time along the direction orthogonal to the direction of the external pulse. With the objective to confirm the existence of the ALF phenomenon and study the geo-mechanical conditions for its occurrence experimentally and theoretically, laboratory tests on granite and cement mortar block models were carried out on a multipurpose testing system developed independently. The ALF phenomenon was realized under two loading schemes, i.e., blocks model and a working block were acted upon jointly by the action of a vertical impact and a horizontal static force, as well as the joint action of both vertical and horizontal impacts with differently delayed time intervals. We obtained the rules on variation of horizontal displacements of working blocks when the ALF phenomenon was realized in two tests. The discrete time delay intervals, corresponding to local maxima and minima of the horizontal displacement amplitudes and residual horizontal displacements of the working block, satisfied canonical sequences multiplied by ( 2 ) i . Some of these time intervals satisfied the quantitative expression ( 2 ) i Δ / V P . At last, 1D dynamic theoretical model was established, the analytical results agreed better with the test data, while the quantitative expression drawn from test data was not validated well in theoretical analyses.

皮膚／木質材料界面における熱挙動のシミュレーション

This paper deals with the simulation of thermal behavior at a boundary between skin and woody materials when the woody materials laid over a cement mortar block are in contact with a man's palm. Plywoods, MDF (medium density fiberboards), and cork boards with different thickness were used as the overlays. Changes in temperature at the skin-overlay-underlayment interfaces were measured with thermo-couples at 10 to 30sec intervals. Furthermore, a thermal transfer model based on a numerical method with finite differences was proposed to analyze the changes in temperature and rate of heat transfer at the interfaces. Thermal constants for the model were obtained by fitting them with the experimental values. Then the changes in temperature and rate of heat transfer were simulated by this model for various overlay materials having different thickness. Not only the model is able to obtain the thermal behavior at the interfaces in good agreement with the experimental results on the samples of various woody materials, but also it is valuable to estimate the sensory warmth felt by man's palm in contact with the surface of the overlays, since both the temperature at the skin surface and the heat transfer across the boundary are highly related with the sensory warmth.

特殊形状薬包によるき裂方向の制御

It is well known that when “Low” explosives are deflagrated in a material, radial cracks are produced from the inner surface of the charge hole. The growing directions of these radial cracks could not be predicted normally, but it might be useful if we could control such growing directions. Therefore, in this paper, the possibility to control the directions of radial cracks has been discussed by using the results of the stress analysis which was undertaken by using the finite element method and also those of the experiments.As the results, it was concluded both theoretically and experimentally that for the case that the material was broken by the quasi-static gas pressure of “Low” explosives, in other words, “Low” explosives of which rate of deflagration was less than about 300m/s were used, the direction of the radial cracks could be controlled by using a specially designed cartridge of which sectional shape was shown in Fig. 1 (a). Namely, the cement mortar block was separated clearly into two parts, as if it was cut out with a knife, by the explosion of a specially designed cartridge of the “Low” explosives of which rate of deflagration was about 100m/s, and no radial cracks towards the undesired directions were observed. Furthermore, the reason why the directions of the cracks were controlled was clarified by the results of the stress analysis.