Cement Mortar Layer Research Articles

The Optimum Interval Time of Layered Cement Composites with the Incorporation of Edge-Oxidized Graphene Oxide

The current research focuses on the effect of incorporating edge-oxidized graphene oxide (EOGO) on the performance of layered cement composites cast at different times. The feature of producing flower-shaped hydrated cement products is exploited to enhance the contact surface of two different cement composites. In the current study, the interval time of casting cement composites is the crucial parameter investigated. Consequently, a layer of cement paste with EOGO is cast above a layer of cement mortar where the amount of EOGO of 0.10% by the cement weight is fixed for all mixtures. Also, four different interval times based on cement setting time are considered, namely immediately, 6 h, 12 h, and 1 day. Similar mixtures are prepared but without adding EOGO for comparison purposes. The results show that EOGO is capable of enhancing the contact surface of layered cement composites by strengthening the split strength of two different layers (between 12 and 29%). Moreover, casting the paste layer containing EOGO after 6 h of mortar layer seems to be the optimum interval time among others by improving compressive strength (by 29%) and residual strength (by 34%) and not affecting flexural strength and porosity percentage.

Comparative analysis of selected machine learning techniques for predicting the pull-off strength of the surface layer of eco-friendly concrete

With recent trends reducing the carbon footprint of concrete, more novel materials are designed. It's mostly done by replacing cement with admixtures that are wastes in industrial processes. There is a need to provide reliable and accurate models to estimate the properties of the material. In this case the selected ML algorithms such as ANN, RF and DT were used for estimating the pull-off strength of the surface layer of cement mortar containing granite powder, fly ash and ground granulated blast furnace slag. The focus was on the cement-sand ratio of 1:3, replacing up to 30 % of the binder. Ultrasonic pulse velocity and pull-off strength of the surface layer. The analyses were performed in comparative manner and proved the accuracy of the designed models. The error values (MAPE, NRMSE and MAE) of the most effective model is below 3,5 %, indicating an extremely high success rate in prediction. An R2 ratio of 0.9436 confirms the very good fit of the model. Parametric tests were performed and SHAP analysis gave a better understanding of the models. The main conclusion of the study is to identify the possibility of replacing destructive testing with non-destructive testing supported by machine learning and material information to determine the pull-off strength of the subsurface layer at a selected depth for cement mortars containing waste materials. A particular advantage of the presented approach is the possibility of reducing the time to determine selected desired material parameters and the amount of testing required compared to the traditional approach.

Integrated design of a robust superhydrophobic cement mortar layer via sizing sand grains

This work reported a facile route for fabricating super-hydrophobic concrete via sizing sand grains. It was found that mixing the sands with a size ranging from 150–180 μm into cement enabled the formation of a lotus-like surface with a papillary structure at micro-scale. SEM showed that the size of bumper was about 3 μm. When spraying a fluorocarbon solution onto this surface, the porous nature of the cement matrix showed the advantage of taking the fluorocarbon into the internal structure of the concrete via capillary force. As a result, the sub surface up to a depth of ∼1.5 mm were transformed into a thick superhydrophobic layer directly. The contact angle (CA) of water droplets could reach 157° on this surface, and which could remain more than 150° after abrasion 100 cycles under a weight of 300 g at 360 grit sandpaper. This thick hydrophobic layer significantly reduced the corrosion rate of the steel the concrete at the Cl- environment by 620 times. The measurement of British pendulum number and compression strength revealed that this superhydrophobic layer was beneficial for maintaining the friction coefficient of the concrete surface in wet condition without altering the mechanical integrity of the concrete.

Influence of Pretreatment Methods on Compressive Performance Improvement and Failure Mechanism Analysis of Recycled Aggregate Concrete.

The utilization of recycled aggregate can avert the squandering of resources and the destruction of the environment. Nevertheless, there exists a slew of old cement mortar and microcracks on the surface of recycled aggregate, which give rise to the poor performance of aggregates in concrete. In this study, for the sake of ameliorating this property of recycled aggregates, the surface of the recycled aggregates is covered with a layer of cement mortar to compensate for the microcracks on the surface and reinforce the bond between old cement mortar and aggregates. In order to demonstrate the influence of recycled aggregate by different cement mortar pretreatment methods, this study prepared natural aggregate concrete (NAC) and concretes with recycled aggregate after the wetting pretreatment (RAC-W) and cement mortar pretreatment (RAC-C), and conducted uniaxial compressive strength tests on different types of concrete at different curing ages. The test results indicated that the compressive strength of RAC-C at a 7 d curing age was higher than that of RAC-W and NAC, and the compressive strength of RAC-C at a 28 d curing age was higher than RAC-W but lower than NAC. The compressive strength of NAC and RAC-W at a 7 d curing age was about 70% of that at a 28 d curing age, and the compressive strength of RAC-C at a 7 d curing age was about 85-90% of that at a 28 d curing age. The compressive strength of RAC-C increased dramatically at the early stage, while the post-strength of the NAC and RAC-W groups increased rapidly. The fracture surface of RAC-W mainly occurred in the transition zone between the recycled aggregates and old cement mortar under the pressure of the uniaxial compressive load. However, the main failure of RAC-C was the crushing destruction of cement mortar. With changes in the amount of cement added beforehand, the proportion of aggregate damage and A-P interface damage of RAC-C also changed accordingly. Therefore, the recycled aggregate pretreated with cement mortar can significantly improve the compressive strength of recycled aggregate concrete. The optimal amount of pre-added cement was 25%, which is recommended for practical engineering.

Experiments and Numerical Simulations on the Seismic Performance of Steel-Frame Composite Wallboard Shear Walls

In order to expand the applications of cold-formed thin-walled steel structures, this study proposes a new type of composite wallboard composed of cold-formed thin-walled C-shaped steel and multi-layer concrete, in which C-shaped steel serves as the skeleton, foam concrete acts as the thermal insulation material, and fine aggregate concrete and cement mortar play the part of envelopes. The composite wallboard can be made in a factory assembly line, meeting the requirements of the building (civil and structural) industry. Two steel-frame composite wallboard shear walls were subjected to reciprocating loading, with the connection mode as the design parameter, to investigate the seismic performance of the structure. The failure mode, hysteresis curve, skeleton curve, strength degradation, stiffness degradation, ductility, and energy dissipation capacity of the specimens were analyzed. On this basis, the finite element (FE) model of the steel-frame composite wallboard was established, and the model’s accuracy was verified by comparing the bearing capacity and the skeleton curve. Results show that the structure shows shear failure characteristics, and the cement mortar layer and the fine aggregate concrete layer are separated from the C-shaped steel after being crushed. The infilled foam concrete is also crushed, and the welding seams between the extended C-shaped steel and steel frame of the WP-1 specimen are damaged. The hysteresis curves of the two specimens have a clear pinch, but the area enclosed by the hysteresis loop is large, and the energy dissipation capacity is also present. The yield load and ultimate load of the WP-2 specimen are higher than those of the WP-1 specimen, indicating that the higher the connection strength between the composite wallboard and the steel frame, the greater the ultimate carrying capacity of the specimen. The established FE model can accurately estimate the seismic performance of steel-frame composite wallboard shear walls.

Recycled concrete aggregate properties improvement

In recent years, there has been increasing interest in the use of recycled concrete aggregate (RCA) as a sustainable alternative to natural aggregates in construction. RCA is obtained by crushing and reusing old concrete, which contains both the original aggregate and a cement mortar layer. However, the quality of RCA can vary depending on the characteristics and quantity of the leftover mortar. In this study, we aim to investigate different methods for improving the chemical, physical, and mechanical features of RCA, with a focus on untreated RCA, RCA exposed to a pre-soaking treatment in HCl, and RCA exposed to rapid carbonation. The overall results show that if RCA is obtained by crushing compact, high-quality concrete, the procedures for improving aggregate quality are not necessary.

A Study on Durability Parameters of Ferrocement

Ferrocement is formed of a thin layer of cement mortar that has been strengthened with multiple layers of wire mesh with a diameter of between 0.5 mm to 1 mm. To evaluate the durability criteria for the specimen, a series of cubes and cylinders were cast in this experiment using a mortar mix at a ratio of 1:3 and a water-cement ratio of 0.40 was selected. In this study, the ability of the ferrocement to endure water penetration, sorptivity, and resistance to sulphates were examined. The curing period was chosen to be 28, 56, and 90 days, respectively, in order to track changes in the outcome and investigate the effects of the various curing times on the ferrocement. In order to measure the rate of water absorption by capillarity rise, Sorptivity test was conducted in accordance with ASTM C1585-04. The average absorption rate at day 9 was found to be 84.87 x 10-7 mm/s1/2, 93.78 x10-7mm/s1/2, and 96.34x10-7 mm/s1/2 for 28, 56, and 90 days of curing respectively. The Sulphate attack test was conducted as per ASTM C 1012-2010. The mass loss was observed to be 0.28%, 0.32%, and 0.33% of the original mass, while the strength loss was 6.96%, 6.44%, and 6.33% for the curing periods of 28, 56, and 90 days respectively. According to DIN-1048, part 5, Water permeability test was conducted. Water was pressured with 500 KPa on the specimen to determine its water penetration. The average water penetration of the specimen was found to be 22.33 mm, 18.67 mm, and 14.33 mm for the corresponding curing periods of 28, 56, and 90 days. The results were within the range twaswere specified in the respective code, and they were judged acceptable in terms of the ferrocement's durability guidelines.

The Effectiveness of a Simulation Model of Thermal Insulation in Building Materials Using Cellulose Extracted from Agricultural Waste in Baghdad

This study found that one of the constructive, necessary, beneficial, most effective, and cost-effective ways to meet the great challenge of rising energy prices is to develop and improve energy quality and efficiency. The process of improving the quality of energy and its means has been carried out in many buildings and around the world. It was found that the thermal insulation process in buildings and educational facilities has become the primary tool for improving energy efficiency, enabling us to improve and develop the internal thermal environment quality processes recommended for users (student - teacher). An excellent and essential empirical study has been conducted to calculate the fundamental values ​​of thermal conductivity coefficient for different types of cement mortar, including the different concentrations of cellulosic fibers. And in our study, those cellulosic fibers obtained from sugarcane and sugarcane residues (agricultural waste materials) were used. The percentage is 10%; 20% and 30% of cellulose fibers were added to the cement mixtures. Then the differences are measured, specifically in the physical properties (heat capacity, density, and thermal conductivity coefficient) for 28 days. The Design-Builder program also implemented a precise simulation of the thermal loads of the external envelope of the educational building that is exposed to direct sunlight before and after the insulation process. It was found that with the use of thermal insulation material (meaning the cellulosic fiber technology) mixed with the cement mortar layer of the educational building, the given value of the heat transfer coefficient W/m2 Kelvin decreased by 47.2%. Accordingly, this contributed significantly to a significant and very significant saving in the values ​​of electrical energy consumption by 11.9% for cooling and heating operations and to reducing dangerous carbon dioxide emissions by 52.2%. The simulation has shown that applying thermal insulation techniques to all buildings and educational facilities is highly recommended to save a large consumption in the value of electrical energy and the costs of waste materials and to ensure integrated protection for the ecosystem.

Dynamic mechanical properties and wave propagation of composite rock-mortar specimens based on SHPB tests

Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens. The results indicate that the transmission coefficient, nominal dynamic strength, interlayer closure, and specific normal stiffness generally increase linearly with increasing interlayer stiffness. The cement mortar layer can serve as a buffer during the deformation of composite specimens. The digital images show that tensile cracks are typically initiated at the rock-mortar interface, propagate along the loading direction, and eventually result in a tensile failure regardless of the interlayer properties. However, when a relatively weaker layer is sandwiched between the rock matrix, an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.

Efficient Use of Graphene Oxide in Layered Cement Mortar.

Graphene oxide (GO) has been found to be an attractive nanomaterial to improve the properties of cementitious composites. However, the use of GO in the industry is limited by its high cost. To achieve a higher cost/performance ratio, GO can be strategically applied in certain parts of cementitious composites structure according to the principle of functionally graded materials. In this study, graded distribution of GO in cement mortar was achieved by sequentially casting a fresh GO-incorporated cement layer on another cement mortar layer. The mechanical properties, especially flexural strength, of layered cement mortar were found to be dependent on the GO content, the delay time, and the interface formed due to layering fabrication. With the GO incorporated in the tensile region only (30% of the total depth), the flexural strength of the layered beam attained 90.91% of that of the beam, with GO uniformly distributed throughout the sample. Based on the results of rapid chloride migration tests, when 12 mm GO-incorporated cement mortar layer was used, the chloride migration coefficient was reduced by 21.45%. It was also found that the measured chloride migration coefficient of layered cement mortar agreed with the series model. The present investigation provides an efficient approach to use GO in cement-based materials from the perspective of mechanical and durability properties.

Analysis of Shaking Table Tests of Underground Structures considering the Influence of the Structure-Soil Interface

To investigate the seismic performance of underground structures under the action of the structure-soil interface, in this study, experiments were performed using plexiglass structures (two pieces) and a concrete structure (one piece) as the research objects. The surface of one plexiglass structure was prepainted with a layer of cement mortar as the contact surface between the structure and soil, and the other plexiglass structure was not treated and used for comparison. A rigid model box measuring 2.25 m × 2.25 m × 1.5 m was placed on a 3 m × 3 m shaking table, and the box was filled with the configured model soil and the underground structure prepared in advance. Input transverse uniform excitation was imparted to the whole system. A shaking table model test was performed on the underground structures to analyse the acceleration response, stress strain, and earth pressure changes in the underground structure, and the influence of the contact surface on the seismic dynamics of the underground structure was evaluated. The test results showed that under uniform excitation, the dynamic characteristics of the underground structures were greatly affected by the intensity and depth of the seismic waves. (1) When the soil-structure contact was considered, the stress and strain of the structures increased significantly, and the stress-strain value was significantly greater than the stress-strain value of the soil-structure interface in a fully bonded state. (2) There were inconsistencies between the acceleration peak curve of the plexiglass structure considering the contact effect and the acceleration peak curve of the plexiglass structure without considering the contact effect. The difference between the two lies mainly in the corresponding maximum peak acceleration and the Fourier spectrum amplitude. With respect to the value and frequency composition, regardless of whether the input acceleration intensity was 0.2 g or 0.5 g, the peak acceleration of the organic structure was greater when the contact surface effect was considered than without the contact surface effect. Therefore, the structure-soil interface needs to be considered in actual engineering. The presence of the contact surface improves the safety of the structure and is helpful for seismic design. The results of this study provide a basis for further research on the influence of soil-pipe contact on the seismic response of underground structures.

Study of mortar layer property of superhydrophobic metakaolin based cement mortar

The use of alternative materials of cement to prepare cement-based materials has attracted more attention to promote the low-carbon and sustainable development in the field of civil engineering. A clean and sustainable method was proposed of preparing cement mortar using metakaolin as an alternative material with suitable mortar layer property. Superhydrophobic metakaolin (SMK), prepared by using a safe and non-toxic method, was added into cement mortar, and its effects on the of the cement mortar layer was investigated. The SMK was found to improve the thickness of the mortar layer and adhesion ability. The SMK increased the cohesiveness of the cement mortar and improved the stability of the mortar layer, thereby increasing the thickness of mortar layer. The results of TGA and SEM show that the SMK rate with less than 2% promoted the hydration of cement, produced additional calcium silicate hydrate and ettringite, and improved the interface transition zone between the aggregate and the cement mortar layer, thereby improving the cement mortar adhesion ability to the aggregate. It is expected that the proposed method may expand the application of superhydrophobic metakaolin in cement-based materials.

Evaluation of performance parameters of cement mortar in semi-flexible pavement using rubber powder and nano silica additives

Semi-flexible pavement offers a high bearing capacity and resistance to rutting. It comprises a layer of cement mortar and one of porous asphalt and is subject to thermal cracking because of the difference in stiffness of these materials. In this study, rubber powder (RP) was used to approximate the stiffness of the cement mortar relative to porous asphalt concrete in order to reduce thermal cracking. Nano silica (NS) was used to reduce the negative effect of RP on the compressive and flexural strength. The effects of these additives on the behavior of 20 mortar mixtures were investigated by mechanical testing and scanning electron microscopy. The results showed that 0.5% to 1% NS can prevent the fluidity loss and increase the drying shrinkage in the matrix. Three of the best-performing mortars were rated, and the optimum mixture was NS1-RP5 containing 1% NS and 5% RP. With an elastic modulus loss of about 20%, it exhibited the best performance and mechanical properties.

Performance of permeable pavement systems on stormwater permeability and pollutant removal

Permeable pavement is an effective means for stormwater runoff control and pollutant removal. However, relatively few studies have examined the characteristics of permeable brick and corresponding permeable pavement system (PPS). In this work, the permeable pavement systems consisted of surface permeable brick layer (concrete or ceramic) with structural layer (including a cement mortar layer, a permeable concrete layer, and a gravel layers) were selected as typical cases to assess their permeability and runoff pollutant removal performance by laboratory experiments. The results indicated that PPS had obvious outflow hysteresis effect. The PPS with ceramic brick layer reached the saturation flow rate earlier and showed larger outflow rate than that with concrete brick layer. Both types of PPSs had a relatively high efficiency (83.8-95.2%) in removing suspended solids (SS) in stormwater runoff mainly due to the interception and filtration of the surface brick layer, whereas the structural layer of the PPS played a vital role in the removal of total phosphorus (TP). The percentage of total nitrogen (TN) removal efficiency via ceramic brick layer accounted for via corresponding PPS was obviously larger than that of concrete brick layer. The PPS also displayed a certain chemical oxygen demand (COD) removal ability: around 14.0-27.0% for concrete type and 20.9-28.9% for ceramic type. Subsequently, a multi-objective evaluation model was implemented based on the analytic hierarchy process (AHP) method to identify the optimal scheme in relation to four indices: permeability, environmental benefit, compressive strength, and comprehensive economic cost. The results showed, insofar, the ceramic PPS is preferred with a better economic performance. Our study attempts to select optimal designs of PPS and provides insight into the permeable capacity and the efficiency of pollutant removal in PPS.

A review of surface properties enhancement of pavement concrete

The surface properties of pavement concrete have great influence on the overall performance of pavement, so it is of great significance to study how to effectively strengthen the surface properties of pavement concrete. The surface properties of pavement concrete are mainly reflected in three aspects: abrasion resistance, frost resistance, and impact resistance. The ways to strengthen the surface properties of pavement concrete are mainly focused on surface fortifier, adding polymer mixture, fiber, and additive, improving the way of maintenance, improving construction technology and optimizing the basic components of concrete. These five ways have its advantages and disadvantages. To enhance the surface properties of concrete economically, effectively and comprehensively, the way that laying fiber mesh into cement mortar layer is put forward.

Functional Method of Designing Self-Compacting Concrete.

The article presents a new functional method of designing self-compacting concrete (SCC). The assumptions of the functional method of designing self-compacting concrete were based on the double coating assumption (i.e., it was assumed that the grains of coarse aggregate were coated with a layer of cement mortar, whereas the grains of sand with cement paste). The proposed method is composed of four stages, each of which is responsible for the selection of a different component of the concrete mix. The proposed designing procedure takes into consideration such a selection of the mineral skeleton in terms of the volumetric saturation of the mineral skeleton, which prevents the blocking of aggregate grains, and the designed liquid phase demonstrated high structural viscosity and low yield stress. The performed experimental studies, the simulation of the elaborated mathematical model fully allowed for the verification of the theoretical assumptions that are the basis for the development of the method of designing self-compacting concrete.

Experimental Study on CFRP‐Confined Circularized Concrete‐Filled Square Steel Tube Short Columns

This study investigates the suitability of the circularization technique for strengthening square concrete‐filled square steel tube (CFSST) short columns. A total of 16 specimens were tested under axial compression. The main parameters under investigation were concrete strength, the thickness of arc cement mortar layer components (CAM), and the layers of carbon fiber‐reinforced polymer (CFRP) sheets. Test results indicated that the failure mode of CFRP‐confined circularized CFSST (C‐C‐CFSST) columns was similar to that of CFRP‐confined concrete columns. The CFRP‐confined circularized strengthening method can increase confinement efficacy and reduce the stress concentration at the corners of CFSST columns. Three existing CFRP‐confined concrete stress‐strain models were evaluated using the test results. The predictions of the Lam and Teng stress‐strain model agree well with the test data.

Durability of cement mortar-covered BFRP bars in simulated seawater environment

To assess the durability of basalt fibre-reinforced polymer (BFRP) bars used to reinforce concrete structures in ocean engineering, the evolution of the thermomechanical properties of cement mortar-covered BFRP bars immersed in simulated seawater environments was studied. The cover thicknesses were set as 10 mm and 20 mm, the immersion temperatures were room temperature (≈28 °C), 40 °C, and 60 °C, and the immersion media were an alkaline solution and distilled water. A set of bare glass fibre-reinforced polymer (GFRP) bars was used for comparison. After one year, the mechanical properties of the bare BFRP bars immersed in a 60 °C alkaline solution deteriorated the most, and the tensile strength decreased from 954.2 MPa to 762.3, 594.7, and 515.5 MPa for the bare BFRP bars and the 10 mm and 20 mm cement mortar-covered specimens immersed in distilled water at room temperature, respectively. The results indicated that alkalinity is a key factor causing the degradation of BFRP and that deterioration is more evident in large-sized cement mortar. In addition, an alkali–aggregate reaction (AAR) of SiO2 in the basalt fibre was evidenced by the presence of a white gel at the interface between the BFRP bars and cement mortar. Thus, AAR is detrimental to the mechanical properties of the cement mortar-covered BFRP specimens in the initial stage. With an increase in immersion time, the cement mortar layer exhibited a protective effect, particularly for the small-sized cement mortar-covered specimens. The BFRP bars are more durable than the GFRP bars owing to the higher fibre volume fraction of GFRP.

Large scale experimental study on bond behavior between polymer modified cement mortar layer and concrete

The effectiveness of concrete structures reinforced by the high strength steel wire mesh-polymer mortar depends on the bond-slip behavior of the interface between the polymer modified cement mortar layer (referred as mortar layer) and the concrete. The areas of the mortar layer tested in the previous studies are generally very small and the obtained conclusions are with limited applications. In this study, the experimental approach was used to analyze the slip behavior of the interface between the concrete block and a larger scale mortar layer. 30 concrete blocks retrofitted with mortar layers were fabricated and the single shear tests on these specimens were conducted. The applied shear loads, slip displacement between the concrete block and the mortar, as well as the strain of the mortar were monitored during tests. The experimental results exhibit the specimens have two representative failure types: debond with and without cracks. Then the bonding performance of the interface was systematically explored by analyzing the failure modes of the specimens and the mechanical property of the mortar. Meanwhile, the slip behavior of the interface influenced by the bond area, the thickness of the mortar layer, the mortar strength and the roughness of the interface were discussed. It was presented that the interface roughness treatment and increasing the mortar strength could significantly improve the behavior of the interface.

Seismic strengthening of masonry walls using bamboo components

Bamboo is a sustainable green material and has been gradually applied in the construction industry; however, little research on strengthening masonry structures with bamboo has been carried out. In this article, strengthening methods using bamboo were developed including bamboo grid reinforced cement mortar layer, externally bonded bamboo mats, additional confining horizontal bamboo reinforced concrete band beams, and bamboo strips placed in mortar joints. Ten masonry walls were designed including two reference walls. Experimental results showed that all the strengthening methods can improve certain aspects of the seismic performance of masonry walls. The shear strength, deformability, and energy dissipation capacity of masonry walls strengthened with bamboo grid reinforced cement mortar and externally bonded bamboo mats were the most improved. The limit states of tested walls were discussed. Strengthened masonry structures with bamboo components are promising methods and can be used especially in remote areas.