Mortar Specimens Research Articles

Mechanism study of the effect of superplasticizers in alkali-activated materials containing sludge

To realize the safe disposal of solid waste containing heavy metals, sewage sludge jointly with slag and metakaolin was used to prepare alkali-activated materials (AAMs), and the effect mechanism of polycarboxylate acid superplasticizer (PCE), naphthalene superplasticizer (NS) and aliphatic superplasticizer (AS) in AAMs were studied. The results showed that both the fluidity and strength of AAMs decreased with the addition of sludge. For the NaOH + Na2SiO3 activated mortar specimen, the incorporation of sludge can reduce their fluidity and strength from 206 mm and 80.25 MPa to 193 mm and 42.43 MPa, respectively. However, the addition of superplasticizers into sludge-containing AAMs leads to a reduction of 3–9% of the fluidity. Interestingly, it can enhance the strength of the AAMs, especially the NS and AS, which increase the strength by approximately 25%. This is attributed to the increase of particle dispersion by superplasticizers. However, the free water released in the process is reabsorbed by the sludge, which increases the local alkali concentration and promotes the activation of the activity. The dispersed sludge particles can play the role of physical filling, making the structure denser. HIGHLIGHTS Sludge is adverse effects on both the fluidity and strength of alkali-activated materials (AAMs). The addition of superplasticizers (SPs) increases the strength of AAM with sludge. SPs do not affect improving the fluidity of AAMs with sludge, even slightly bad. The dispersion effect of SPs on the sludge is beneficial to promote its activity in AAMs.

Embeddable Chloride Sensor for Monitoring Chloride Penetration into Cement Mortar.

A composite solid chloride sensor consisting of two single sensors, i.e., Ag/AgCl working electrode and Mn/MnO2 reference electrode, was developed. The Ag/AgCl electrode was prepared by the anodic polarization method, while the Mn/MnO2 reference electrode was prepared using the powder compaction technique. Then, the electrochemical performances such as stability, reproducibility, and sensitivity of the composite and single sensors were investigated in a saturated Ca(OH)2 solution and mortar specimen. A current density of 0.5 mA/cm2 and polarization time of 2.5 h were the optimal preparation parameters of the Ag/AgCl selective electrode. The Ag/AgCl selective electrode showed a linear potential response with the logarithm of chloride ion content in solution and had good stability, reproducibility, and anti-polarization performances. In addition, the Mn/MnO2 electrode exhibited potential stability after being activated in an alkaline solution for 60 days. The composite sensor demonstrated exceptional sensitivity to the Cl- content, boasting a slope of approximately 51.1 mV/decade, and showcased excellent stability in both solution and mortar specimens. In every measurement, the time needed for the potential of a composite sensor to become stable was less than 30 s. The sensor enables non-destructive in situ monitoring of the chloride ion content in cement mortar, thus realizing early warning of deterioration of reinforcement and guaranteeing long service life of the structure.

Impact of internal pre-damage due to drying shrinkage under various humidity conditions on DEF expansion in cement paste and mortar

This study explores the impact of internal pre-damage from early drying shrinkage on the delayed ettringite formation (DEF) expansion behavior of cement-based materials subjected to high-temperature processes. Specimens of cement paste and mortar with water-cement (W/C) ratios of 0.4, 0.5, and 0.6 were characterized after curing under relative humidity (RH) conditions of 50, 70, and 100 for 56 days. The parameters assessed were drying shrinkage, dynamic elastic modulus, and free water content. Subsequent DEF expansion over time was quantified, and the underlying mechanism was analyzed using XRD and SEM techniques after 270 days of underwater curing. Results indicate that: (1) a lack of adequate early curing humidity significantly reduces the dynamic elastic modulus with more than a 10% drop in cement paste following 56 days at RH50; (2) a higher W/C ratio and lower early curing humidity lead to more internal damage due to shrinkage, thereby promoting DEF expansion; (3) drying intensifies internal pre-damage in the interfacial transition zone (ITZ), causing an earlier deterioration of DEF expansion in mortar compared to cement paste. However, the presence of aggregates constrains this, leading to lesser DEF expansion in mortar; (4) dynamic elastic modulus changes as measured by ultrasonic methods can quantitatively characterize the extent of deterioration caused by DEF expansion, thus offering a tool for non-destructive testing and DEF expansion deterioration analysis.

Enhanced Microwave Deicing Capacity of Cement Pavement with Carbon Fiber Screens.

The combination of an absorbing structure and a road is a promising strategy for road deicing using microwaves. In this study, cement mortar (CM) specimens containing a carbon fiber screen (CFS) were prepared to concentrate electromagnetic losses on a road surface. The effect of the size and depth of the CFS on the surface heating efficiency of the microwave was studied and optimized, and a microwave deicing experiment was conducted. The results indicated that the destructive interference produced by the CFS led to the effective surface heating of the CM/CFS specimens. The optimal surface heating rate was 0.83 °C/s when the spacing, depth, and width of the CFS were 5.22, 13.31, and 2.80 mm, respectively. The deicing time was shortened by 21.68% from 83 to 65 s, and the heating rate increased by 17.14% from 0.70 to 0.82 °C/s for the specimen with CFS-1, which was 15 mm depth. Our results demonstrate that CM/CFS composite structures can be effectively applied to increase the capacity and accelerate the development of the microwave deicing of roads.

Effect of Lithium Mica Slag on the Internal Sulfate Attack of Cement Mortar

Lithium mica slag is a byproduct acquired via the sulfate method of lithium extraction, and it contains a certain quantity of soluble sulfates. The improper storage of lithium mica slag not only takes up a large amount of land resources, but also poses a threat in terms of environmental pollution. Therefore, this study aimed to investigate the mechanism by which SO42− dissolves in lithium mica slag, along with the impacts of internal sulfate attacks on mortar specimens with 10%, 20%, and 30% lithium mica slag contents. Testing was carried out in terms of the expansion, mass change, flexural and compressive strengths, porosity, composition, and contents of the products. It was determined that a significant quantity of SO42− was generated in mortar specimens with lithium mica slag. The mortar specimens mixed with lithium mica slag produced more ettringite (AFt: 3CaO·Al2O3·3CaSO4·32H2O), which is the product of internal sulfate attacks. This demonstrates that there was an internal sulfate reaction in the mortar specimens mixed with lithium mica slag. The internal sulfate reaction in mortar samples with lithium mica slag was finished in the later stages. It is noteworthy that the reaction did not lead to any cracking or damage; instead, it later allowed for a retention of strength that was equivalent to the strength of mortar specimens without lithium mica slag. In addition, the partial replacement of cement with lithium mica slag not only reduced the environmental pollution caused by soluble sulfates in lithium mica slag, but also reduced the use of cement and, thus, lowered costs.

Preliminary study on double-sided direct shear test of microbial mortar

A new method of strengthening masonry structures of ancient architecture has been proposed, which involves the use of microbial grouting to generate mineralized mortar. To study the shear mechanical properties of microbial mortar, a comparative experiment was designed with 9 groups of specimens, including acid washing method to test the amount of calcium carbonate, penetration method to test compressive strength of mortar, double-sided direct shear method to test shear strength of mortar and get shear stress-strain curve. According to the experimental results, when the brick joint is thick, more bubbles remain at the contact between the brick and the mortar, reducing the saturation of the grouting liquid and affecting the amount of calcium carbonate generated, thereby affecting the shear strength of the mortar. When the brick is placed vertically, the contact area between the brick and the mortar is on the side, and it is not easy for bubbles to remain, so the amount of calcium carbonate generated is high, and the corresponding shear strength of the mortar is high. Reducing the concentration of calcium solution and implementing bidirectional perfusion can slow down the deposition of calcium carbonate and blockage of perfusion pathways, thereby improving the homogeneity of the carbonate level. A well-graded filling of sand particles is an effective measure to improve the binding efficiency of calcium carbonate.These measures not only increase the production of calcium carbonate, but also result in higher compressive and shear strength.The shear stress-displacement curve of microbial mortar specimens with damagedmortar layer exhibits strain-softening behavior, while the specimens with inter facial damage show strain-hardening behavior.The shear strength of specimens with interface damage is lower than that of specimens with mortar layer damage, so measures should be taken to avoid interface damage.

The mechanical properties of the interface between concrete–epoxy mortar: Splitting tensile vs. direct shear testing

This study investigated the effects of low-temperature curing environment, moisture content of concrete, and surface roughness of concrete on the interfacial bond performance of concrete–epoxy mortar composite specimens. The mechanical and microstructural properties of concrete–epoxy mortar composite specimens were studied systematically via splitting tensile strength test, direct shear strength test, and scanning electron microscopy test, and the failure modes were observed. Further, the factors that remarkably affect the mechanical properties of the concrete–epoxy mortar composite specimen were investigated by analysing the images obtained using grey correlation analysis. The results indicated that the compressive strength of epoxy mortar, interfacial splitting tensile strength, and shear strength of composite specimens decreased gradually with the decrease in curing temperature. The splitting tensile strength and shear strength at the interface of the composite specimens first increased and then decreased with increasing surface roughness of the concrete. However, these parameters gradually decreased with the increase in moisture content. Moreover, based on the results of grey correlation analysis the three factors, the curing temperature had the most influence on these two strengths, followed by surface roughness and then moisture content. In this case, the surface roughness and moisture content have a comparable degree of influence. The relationship between shear strength and splitting tensile strength was investigated and a good linear relationship was found between these two parameters. The microstructure performance analysis show that as the curing temperature decreased, pores appeared around the foundation concrete. Consequently, the aggregate structure became loose, and the overall denseness was remarkably reduced. As the moisture content of the concrete increased, the pores and cracks at the interface increased, and the width of the interface transition zone became larger.

Cementitious properties of coal-based metakaolin prepared from coal gangue via Fe3O4-Assisted microwave activation

Coal gangue is the largest emission of solid waste in the coal industry, and its large accumulation has posed serious hazards to environment. Low-quality coal gangue can be transformed into an auxiliary cementing material (coal-based metakaolin) with pozzolanic activity after calcination. However, the conventional calcination has slow heating rate, high energy consumption and serious pollution issues. Therefore, the fast and efficient calcination of coal gangue must be explored. In this study, coal series kaolinite (coal gangue with a kaolinite content of more than 80%) from Inner Mongolia was calcined by Fe3O4-assisted microwave calcination craft to prepare coal-based metakaolin (CBM). Results indicated that the efficiency of the microwave calcination of coal series kaolinite powder (CSKP) was considerably increased by adding analytical-grade Fe3O4 to CSKP. After substituting 30% of cement with CBM prepared by Fe3O4-assisted microwave calcination of CSKP to prepare cement–coal based metakaolin mortar (CCBMM), the mortar specimen made of CBM prepared at 675 °C showed the highest compressive strength (61.3 MPa) and activity index (112%). The analytical-grade Fe3O4 particles in CSKP will form spherical hematite microparticles (Fe2O3) with good dispersion after microwave calcination at appropriate temperatures (650 °C and 675 °C), which acted as microaggregates to optimize the pore structure of CCBMM, thereby enhancing the strength of CCBMM. The findings of this study confirmed that analytical-grade Fe3O4 addition not only increased the efficiency of preparing CBM by microwave calcination and reduced energy consumption, but also improved the cementitious performance of CBM.

Development of piezoelectric impedance-based technique for rapid compressive strength measurement of mortar specimen using artificial neural network

Measurement of concrete strength is crucial for both the construction and maintenance stages of infrastructures. This importance is emphasized every year in Korea, where aging facilities require reliable and accurate assessment to prevent accidents. In general, three types of non-destructive testing methods are used for concrete maintenance, including the ultrasonic and rebound hardness methods, with a combination method also used. However, despite the popularity of these methods, there can be reliability issues as these methods estimate the strength of concrete through equations, rather than direct measurement. In this study, a non-destructive testing method known as the electromechanical impedance technique is used to predict the compressive strength of two different mortar specimens of 10 MPa and 30 MPa with the use of artificial neural network. In addition, the conventional method of permanently attaching the piezoelectric transducer was altered in a way to achieve temporary attachment to the host structure to make the proposed idea more useful for real field. The result from the experiments proves the possibility of predicting the difference in the compressive strength of the two mortar specimens.

High-temperature behavior of zeolite-containing mortar. Experiment and modelling

High temperature experiments were carried out on cylindrical-shaped specimens of mortar containing different concentrations of either cement-replacing zeolite or aggregate-replacing zeolite. The behavior was compared with that of plain mortar. Furthermore, finite-element models were designed, based on material characteristics obtained on the real specimens, to test the temperature exposure effect when similar conditions were applied.

The Use of Artificial Neural Network for Predicting the Thermal Conductivity of Cement Based Mortar with Natural Zeolites

Zeolites, in their natural state, have been used in construction materials since ancient times. The pozzolanic activity of zeolites and their use as supplementary cementitious materials has been investigated over the past three decades. The indoor comfort provided by a modern life style comes at a cost of consuming enormous amounts of energy. Materials with improved insulation properties are continuously researched and the use of zeolites showing encouraging results. The paper presents experimental results obtained on different cement-based mortar mixes incorporating natural zeolites. The main parameters of the research were: substitution of cement and sand by natural zeolites, three different replacement percentages for cement and sand (10%, 20% and 30%) and the curing age of mortar specimens (14 days, 21 days and 28 days). An artificial neural network (ANN) was developed to predict the values of the thermal conductivity by taking into account parameters such as density, humidity and surface temperature of the mortar samples. The ANN was able to accurately predict the experimental results for the thermal conductivity of cement-based mortars with natural zeolites.

Evaluation of Hydrothermally Treated Wood Fibre Performance in Cement Mortars

Biofibres’ wide application in mortar enhancement has thus far been restricted by factors related to their chemical composition and hygroscopic nature. Their hydrophilic behaviour increases the water demand of mortar mixtures and diminishes their affinity to the matrix, while further moisture-related fibre degradation issues may arise. Additionally, natural fibres seem to be susceptible to degradation caused by exposure to alkaline environmental conditions such as those experienced by cement mortars, restricting their utilisation in the construction industry. Therefore, the current study investigates the potential of fibre modification through treatments that would permanently alter their structure and chemical composition to improve their performance. In this study, wood fibres of black pine and beech species were exposed to mild thermal treatment (140 °C 2 h, under a steam atmosphere), characterised in terms of the physical and chemical properties and incorporated in cement mortars, applying the proportion of 1.5% v/v in the mortar, in order to assess their performance as reinforcement material. The mortars’ workability (at a fresh state) was examined, as well as other physical, hygroscopic, thermal, and mechanical characteristics of the mortars at the ages of 28, 90 and 365 days and weathering performance, by subjecting them to different artificial ageing environments (freeze–thaw cycles or outdoor exposure). The results revealed the beneficial role of the treated fibres in dimensional stability, flexural strength, thermal insulation properties and capillary absorption of the mortar specimens, especially during the ageing process, with the black pine fibres showing the greatest improvement. The hydrothermally treated wood fibres seem to help maintain the integrity of cement mortars under all ageing conditions, proving that they could provide low-cost and eco-friendly mortar enhancement pathways.

Experimental investigations on water sorptivity in mortars with the use of X-ray micro-CT system

The phenomenon of water sorptivity in prismatic mortar specimens was investigated in this experimental work. This phenomenon is closely linked to material durability. Sorptivity evaluated during a steady stage, combined with exposure conditions can be used for performing service life predictions. Water's initial and secondary sorptivity in unsaturated mortar specimens were measured in laboratory tests following the standard ASTM C 1585–04. The impact of initial porosity on sorptivity was investigated by varying the cement-to-sand ratio (c/s) and the water-to-cement ratio (w/c). In addition, the surface area of water intake was changed which was either vertical or horizontal in orientation. The water distribution in the test specimens was visualized using the 3D X-ray micro-CT system SkyScan 1173 which was a novelty. The mortar sorptivity was found to be highly responsive to the c/s ratio, varying by up to 100%, and to be moderately impacted by the w/c ratio, varying by up to 25% and the surface inflow direction, varying by up to 45%. The sorptivity increased with a decline in the c/s (in agreement with the existing literature data) and w/c ratio (in contrast with the existing literature data). According to micro-CT images, the water distribution in the specimens was found to be non-uniform and larger porosity contributed to the rise in water level but not to the total volume of absorbed water (in contrast to the literature data). The snap-off events were detected ahead of the waterfront.

Revealing the Proximity of Concrete Specimens to Their Critical Damage Level by Exploring the Cumulative Counts of the Acoustic Emissions in the Natural Time Domain.

This study aims to explore the possibility of detecting indices that could potentially provide warning about the proximity of internal damage to critical levels, beyond which catastrophic fracture is impending. In this direction, advantage was taken of the Cumulative Counts that were recorded during the mechanical loading of specimens made of either plain or fiber-reinforced concrete. The parameter adopted for the analysis was the average rate of change in the Cumulative Counts. Τhe evolution of the specific parameter was considered in the Natural Time Domain, rather than in the conventional time domain. Experimental data from already published three-point bending protocols were used. It was revealed that the specific parameter attains, systematically, a limiting value equal to unity exactly at the instant at which the load reaches its maximum value, which is not identical to the load recorded at the instant of fracture. Similar observations were made for a complementary protocol with uniaxially compressed mortar specimens. The conclusions drawn were supported by the b-values analysis of the respective acoustic data, again in terms of Natural Time. It is, thus, indicated that the evolution of the average rate of change in the Cumulative Counts in the Natural Time Domain provides an index about the proximity of the applied load to a value beyond which the specimen enters into the critical state of impending fracture.

Effects of Dosing and Mechanical Activation on the Performance of Reservoir Sediment-Cement Composite Cementitious Material

To solve the problem of reservoir sediment accumulation, this paper intends to study the feasibility of preparing reservoir sediment-cement composite cementitious material by partially replacing cement with reservoir sediment. Using the single factor test method, the replacement rate of reservoir sediment and mechanical activation time were selected as variables to explore the effects of water requirement of normal consistency, setting time, mortar fluidity, and mechanical properties of mortar specimens. The results show that with the increase of sediment replacement rate, the water requirement of normal consistency of composite cementitious material paste increases, the setting time increases, the fluidity of mortar decreases, and the mechanical properties of mortar specimens decrease significantly. With the increase of mechanical activation time, the water requirement of normal consistency decreases, the setting time decreases, the fluidity of mortar increases, and the mechanical properties of the mortar specimen increase. The microcosmic results show that mechanical activation can promote the formation of C-S-H gel in reservoir sediment, and fill each other with unreacted reservoir sediment particles, resulting in a denser microstructure. The purpose of this paper is to provide theoretical support for the preparation of reservoir mud-cement composite cementitious material.

Mechanical properties of thermally damaged mortar under coupled static-dynamic loading

In buildings that experience fires, cement mortar is subjected to high-temperature environments and not only the weight of the structure above but also blast loads, leading to structural damage and loss of load-bearing capacity. To investigate the static and dynamic mechanical properties of thermally damaged mortar, a series of tests utilizing modified split Hopkinson pressure bar were conducted. These tests included quasi-static, conventional dynamic and coupled static-dynamic loading tests on mortar specimens that were subjected to seven temperature levels: 20°C, 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C. The test results revealed that both the thermal damage and loading method had an impact on the mechanical properties and damage characteristics of the mortar specimens. The compressive strength, elastic modulus and absorbed energy ratio of mortar decreased as temperature increased. Notably, the quasi-static strength loss rate was 60% when the temperature reached 600°C. Under coupled static-dynamic loading, the specimens exhibited higher strength, elastic modulus, reflected energy ratio, and transmitted energy ratio. Conversely, they had lower average strain rates and absorbed energy ratios. Intriguingly, the dynamic growth factor had a relative increase of 0.7–2.0 compared with other loading methods. Furthermore, the higher temperature, the higher fragmentation of the specimens in the fragmentation pattern. Conventional dynamic loading resulted in the greatest degree of fragmentation. The findings provide a scientific basis for the design and evaluation of concrete shockproof and explosion-resistant structures.

Optimizing geopolymer mortar for shotcrete applications by focusing on flowability and early-age mechanical characteristics

To facilitate the use of geopolymer materials in shotcrete applications, this study presents the development of a geopolymer mortar and explores its flowability and early-stage mechanical properties. Firstly, 15 groups of geopolymer mortar specimens with 3 liquid-binder ratios (0.70, 0.75 and 0.80) and 5 binder-aggregate ratios (0.225, 0.250, 0.275, 0.300 and 0.325) were developed. Secondly, the P-wave velocity, slump, early-age compressive strength and compressive strength were obtained by ultrasonic pulse velocity test, slump test and uniaxial compressive test. Thirdly, discussion on the effect of liquid-binder ratio and binder-aggregate ratio on P-wave velocity, flowability, compressive strength and early-age compressive strength of geopolymer mortar were carried out. Finally, an optimal mix proportions rang of geopolymer mortar materials that meet the requirements of wet shotcrete technology were proposed. The results show that P-wave velocity, slump, early-age compressive strength and compressive strength increase as the increasing of liquid-binder ratio. The slump, compressive strength and P-wave increase as the increasing of binder-aggregate ratio. Moreover, the optimal binder-aggregate ratios were proposed as 0.244 - 0.321, 0.228 - 0.298, and 0.209 - 0.241 for geopolymer mortar with a liquid-binder ratio of 0.70, 0.75 and 0.80, respectively. Geopolymer mortar in these mix proportions achieves compressive strengths ranging from 28.4 MPa to 41.1 MPa after curing for 1 day and 44.2 MPa to 55.4 MPa after curing for 28 days. The mix proportion of geopolymer mortar proposed in this paper can simultaneously meet the standard requirements for mechanical properties and flowability, demonstrating potential for wet shotcrete applications.

Properties of Cement Mortars Made With Local Steel Slag

As a way to reduce the impact of the cement industry and reduce its production cost, researchers have studied to use by product materials such as fly ash, silica fume and slag as a partial replacement for Portland cement in the making of concrete. In this study, the effect of partial cement replacement with Libyan electric arc furnace steel slag in different substitution levels (0, 10, 20 and 30% by weight) were investigated using cement mortars. Slag of 350 m2/kg Blaine fineness was used in this study. The mortar specimens were tested for compressive, flexural and direct tensile strengths at the ages of 3, 7, 28, 56 and 90 days. The effect of slag content on mortar workability was studied. Setting times and soundness of cement paste were also investigated.The experimental results showed that replacement of cement by slag causes delay in cement setting times. Setting times increases as the slag content increases. The results also showed that compressive, direct tensile and flexural strength of mortar improves with time and the development in strengths is influenced by the slag content. The addition of 10% electrical arc furnace slag (EAFS) has positive effect on compressive, tensile and flexural strengths of mortar at late age.

Dynamic compressive behaviors of high-temperature-cement mortar specimen subjected to different cooling methods

Impact load and rapid cooling, which frequently appear in fire-fighting and explosion, are major factors to affect the stability of cement mortar structures. By carrying out the dynamic compressive and scanning electron microscope experiments on high-temperature-cement mortar specimen subjected to rapid cooling with different cooling methods, the dynamic compressive behaviors and internal structures were studied and discussed. The results show that both the strain and cooling rates affect dynamic properties. In details, dynamic compressive strength, which could be calculated by linear Function with strain rate, shows an increase trend when strain rate and cooling rate increase. On the contrary to the change of strength, the size of failure pieces decreases. The specimen breaks more thoroughly with increasing strain and cooling rates. The dynamic elastic modulus, which shows an decrease trend accordingly as cooling rate increases, shows inconspicuous change with strain rate. Comparison with untreated specimen, there are more failure paths during the compressive process, especially, when the specimen is treated with rapid cooling, the phenomenon is more evident. The thermal stress caused by cooling leads to the increasing size and number of cracks, even the cracks connecting with each other and forming into crack-system, which finally results in the weakening of dynamic properties.

Gelatin‐based air‐entraining agents for ordinary portland cement: Chelate Ca2+ and reduce surface tension

AbstractIntroducing uniform, stable, and small pores by adding air‐entraining agents (AEAs) is an effective strategy for improving the freeze–thaw resistance and workability of cement concrete materials. In this study, the gelatin with hydrophobic and hydrophilic functional groups was used as an AEA for cement concrete materials and systematically studied its effect on the performance of cement mortar specimens. The results showed that gelatin has a surfactant‐like function and can effectively reduce the surface tension of the gas–liquid interface. In an alkaline environment, Ca2+ ions in cement pore solution chelate with carboxylate ions formed by carboxyl ionization, further enhancing the performance of gelatin‐based AEAs. Thanks to the reduction in surface activity and carboxyl ionization, introducing gelatin increased the porosity of cement mortar specimens from 0.53% to 2.69%. Furthermore, introducing an appropriate amount (>0.1 wt%) of gelatin does not significantly impact the workability or mechanical properties of cement mortar. Based on these characteristics, gelatin has potential as an AEA for cement concrete materials.