Type Of Cementitious Material Research Articles

Experimental and numerical simulation studies of electrical resistance of cementitious materials under varying temperature history

Many in-service concrete structures are normally exposed to varying temperature condition. The time-dependent and non-uniform temperature distribution in concrete structures could affect the accurate assessment of their electrical properties. Therefore, the influences of temperature change over time and the spatial variation in temperature on the measured electrical resistance of cementitious materials are still in need of investigation. The coupled thermal-electrical responses of two types of cementitious materials under varying temperature history were investigated by a series of thermal and electrical tests in this study. Then a coupled thermal-electrical finite element (FE) model was developed to simulate the coupled thermal-electrical responses. The results show that the input direct current has a minor effect on the measured electrical resistance by embedded four-probe method and the specimen temperature when it is no greater than 3 mA. The relationship between the measured temperature at 10-mm depth of the specimen and the apparent resistance is well captured by a linear equation. The coupled thermal-electrical finite element model can predict well the developments of specimen temperature and apparent electrical resistance under varying temperature history. The FE results reveal that the non-uniform temperature variation results in the redistribution of electrical current within the tested specimen. However, electrical field between the two inner electrodes is always uniform when the embedded four-probe method is used, which is not affected by the non-uniform temperature variation.

Determination of engineering properties of cementitiously stabilised aggregates using ultrasonic pulse velocity

Non-destructive testing methods, such as Ultrasonic Pulse Velocity (UPV), have been widely used to assess the quality and performance of cementitious stabilised aggregates. The present study reveals the robust relationship of UPV and constrained modulus (CM) with unconfined compressive strength (UCS), modulus of rupture/flexural strength (MoR), and flexural modulus (FM) in aggregates stabilised with five different stabiliser combinations, including cement, cement-ground granulated blast furnace steel slag (GGBS), cement-fly ash and cement with two commercial chemical admixtures. The high accuracy of UPV and CM in estimating destructive test parameters and approximating challenging tests like FM is convincingly demonstrated with strong correlations (R² > 0.80) and standard error ratios (Se /Sy < 0.35). Power law and logarithmic curves prove suitable for modelling the relationships between strength and stiffness with UPV and CM, respectively. Notably, however, the study reveals significant variations in correlating parameters across different cementitious stabilisers within the same mix design, emphasising the strong dependence on the specific cementitious material type. Overall, this work offers valuable insights into the use of non-destructive parameters, UPV and CM, for the characterisation of stabilised aggregates based on cementitious material type and different curing conditions.

Effect of sulfate on the compatibility between polycarboxylate superplasticizer and cement-based materials with or without silica fume

Polycarboxylate superplasticizer (PCE) is a crucial raw material used for preparing concrete. However, there has always been a compatibility issue between PCE and different types of cementitious materials due to their varying qualities. In concrete raw materials, the types and contents of sulfates have a significant impact on compatibility, and it is well-established that a competitive adsorption exists between PCE and sulfate ions solubilized in the interstitial solution of cement paste, which may cause a loss of the dispersing properties. However, previous studies focused on the effect of sulfate on the compatibility between PCE and cement, and there was a lack of research on silica fume. In this study, the workability of fresh cement and cement-silica fume paste and the mechanical properties of harden mortar were evaluated in the presence of different concentrations of five types of sulfates (Na2SO4, K2SO4, MgSO4, KAl(SO4)2, and CaSO4·2H2O) added in aqueous solution. The results show that soluble sulfates have a more adverse effect on the compatibility between PCE and cement-based materials with or without silica fume than slightly sulfate. And the effects of different sulfates on saturation points of PCE in cementitious materials and the mechanical properties of cement and cement-silica fume mortar are various. Finally, it is important to note that a high sulfate content in the solution can lead to salt precipitation of PCE, which is highly undesirable.

Effect of silt modification on the properties of magnesium phosphate cement

Magnesium phosphate cement (MPC), as a new type of cementitious material, is difficult to be popularized in practical applications due to its short setting time, high cost, and poor water resistance. Dredged silt (DS) is a kind of hazardous waste, which may cause serious damage to the ecological environment if it is not disposed of properly. The treatment of DS and its reuse in building materials is an economical and environmentally friendly treatment method, which not only realizes the recycling of DS but also avoids secondary pollution. Using the treated DS as a mineral admixture for modified MPC not only recycles the DS but also improves the properties of MPC. In this paper, the effect of DS modification on the properties of MPC was investigated by setting time test, mechanical property test, water resistance test, and RCM test, and also compared with the modification effect of common mineral admixtures, such as fly ash (FA) and metakaolin (Mk), and finally analyzed by combining with SEM pictures. With the increase of the dosage of FA, Mk, and DS, the compressive strength of the modified MPC all showed the trend of increasing and then decreasing, and the optimal dosage was 5%, 10%, and 15%, respectively. At the optimum dosage, Mk and FA could improve the resistance of MPC to chloride erosion, but DS could not. The three kinds of admixtures could prolong the setting time of MPC, with DS having the best effect, followed by FA, and Mk having the smallest effect. All three admixtures could improve the water resistance of MPC, and the effect of improvement was Mk &amp;gt; DS &amp;gt; FA. The microstructure of the specimen was denser when the dosage of DS was low, and when the dosage was too much, the hydration reaction of MPC was affected, resulting in incomplete hydration and reduced hydration products. This research has significant guiding significance for the treatment of DS and the modification of MPC.

Geopolymer vs ordinary portland cement: review of the 3-d printing of concrete

Due to the need of the construction industry to implement structures with special and complex designs, mass customization with the lowest cost, especially reducing the labor cost as well as the amount of waste and materials used, the use of concrete 3D printing can be the appropriate solution to these requirements fulfill these options. As a result, a comprehensive and practical study of the major 3D printing methods and their development in the construction industry was carried out in this study. In addition, the use of OPC-based materials and geopolymer-based materials was reviewed and compared due to the development of the materials industry and the advantages and disadvantages of using different types of cementitious materials in the 3D printing of concrete.

Recent development on optimization of bio-cementation for soil stabilization and wind erosion control

This paper reviews and analyzes recent research development on bio-cementation for soil stabilization and wind erosion control. Bio-cement is a type of cementitious materials by adopting natural biological processes for geotechnical and construction applications. Bio-cementation is usually achieved through microbially- or enzyme-induced carbonate precipitation (MICP or EICP). The use of soybean urease can be a cost-effective solution for carbonate precipitation and bio-cementation, which is named SICP. The produced calcium carbonate can cement soil particles and bring considerable strength improvement to soils. In this paper, the mechanisms and recent development on the technology optimization are reviewed first. The optimization of bio-cementation involves 1) altering the treatment materials and procedures such as using lysed cells, low pH, the salting-out technique; and 2) using cheap and waste materials for bio-cement treatment and bacterial cultivation. The objectives are to improve treatment uniformity and efficiency, use bio-cement in more scenarios such as fine-grain soils, and reduce costs and environmental impacts, etc. Studies on the mechanical behaviour and wind erosion performances of bio-cemented soil show that the wind erosion resistance can be improved significantly through the bio-cement treatment. In addition, the use of optimized method and additives such as xanthan gum and fibers can further enhance the strength, treatment uniformity or ductility of the bio-cemented soils. Attention should be paid to wind forces with saltating particles which have much stronger destructive effect than pure wind, which should be considered in laboratory tests. Field studies indicate that bio-cement can improve soil surface strength and wind erosion resistances effectively. Besides, local plants can germinate and grow on bio-cemented soil ground with low-concentration treatments.

A comprehensive review on the properties of engineered cementitious composite with a self- healing material

The most common types of cementitious materials used as building materials can be found all over the world. The fact remains, however, that deterioration is unavoidable right from the start of the service life, which is followed by maintenance and repair work. Since the cementitious materials have been observed to exhibit a self-healing phenomenon, which has been the subject of research for quite some time. This paper is focused on the review of the feasibility of (Engineered Cementitious Composite) ECC and its properties such as mechanical, physical, rheological, and chemical properties. ECC is considered to have a high self-healing potential and superior mechanical and durability performance. Self-healing concrete is typically employed for the purpose of minimizing cracks in concrete and enhancing the material's overall durability. These mechanisms are reviewed based on extensive experimental studies and practical experience. Self-healing concretes are typically employed for the purpose of mending cracks in concrete and enhancing the material's overall durability. There are many distinct varieties of self-healing processes, including natural, chemical, and biological ones. Studies were conducted with a primary emphasis on biological processes that are dependent on precipitation. In order to study the properties of self-healing with ECC, a transmission electron microscope (TEM), an environmental scanning electron microscope-energy dispersive spectroscopy system (ESEM-EDS), Fourier transform infrared spectroscopy, and X Ray Diffraction (XRD) were all implemented. To further understand the properties of self-healing, this research was conducted. This review offers a fresh perspective on the research done on the topic of treating unexpected cracking in concrete through the use of a self-healing process.

Hydration characteristics, hydration products and microstructure of reactive powder concrete

Reactive Powder Concrete (RPC) is a new type of cementitious materials with a complex hydration mechanism, and active admixtures greatly influence the hydration reaction, formation of hydration products, and evolution of microstructure. In order to comprehensively study the quantitative effects of active admixtures contents, namely silica fume, slag and fly ash, on hydration characteristics, hydration products, and microstructure of RPCs, tests of workability, setting time, electrical conductivity, bound water and mechanical properties were conducted. Furthermore, a series of properties including morphology and micro-structure characteristics of RPCs were analyzed by thermogravimetric (TG) analysis, X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), mercury intrusion porosimetry (MIP), Brunauer-Emmet-Teller (BET), and scanning electron microscope (SEM). The results indicate that the initial hydration reaction rate of RPCs is reduced by partly replacing cement with active admixtures. The pozzolanic effect created by the active admixtures enhances hydration and improves RPC's compressive and flexural strength. RPCs made of cement-silica fume mixture exhibit the best macroscopic properties. The adoption of silica fume promotes the production of C–S–H gel during hydration and exerts pozzolanic and crystal nucleation effects to promote cement hydration. RPCs made of pure cement exhibit 15.3% porosity after 28 days of hydration, with the largest proportion of less harmful pores in the microstructure. The porosity is reduced to 5.2% when cement is partially replaced with silica fume, and the microstructure is dominated by harmless pores. When replacement of silica fume is kept at 25%, using slag powder or fly ash substitute part of cement also reduces the number of less harmful pores. It is beneficial to add slag powder to increase the number of gel pores, whereas fly ash reduces the number of gel pores. The investigation presented in this paper would contribute to the production of low cost and environmentally-friendly RPCs, and accelerate the wider applications of ultra-high performance concrete (UHPC) in engineering structures.

Cyclic Behaviors of Geopolymeric Recycled Brick Aggregate Concrete-Filled Steel Tubular Column

Incorporating geopolymeric recycled brick aggregate concrete into steel tubes provides a promising solution to reduce environmental impact of construction and demolition waste. In this paper, geopolymeric recycled brick aggregate concrete-filled steel tubular column (GRBACFST) was developed to improve the environmental sustainability of composite column. Considering the replacement ratio of recycled brick aggregate (RBA), the thickness of the steel tube, type of cementitious materials and the axial compression ratio as the variation parameters, experimental research was performed to explore the cyclic behavior of GRBACFST columns, including the failure mode, bearing capacity, hysteresis curve, ductility and degradation characteristics. Results demonstrated that the failure of GRBACFST columns occurred in the region at column bottom, with the bulge of steel tube and crush of geopolymeric recycled brick aggregate concrete. The proposed GRBACFST columns exhibited favorable hysteretic behaviors with desired bearing capacity, excellent ductility, and energy dissipation behavior, which were enhanced by the increased thickness of the steel tube. The bearing capacity and ductility were reduced with the increase of axial compression ratio, while enhanced with thicker steel tube. Moreover, the degradation of stiffness and strength was more obvious under larger axial compression ratio. The increase of replacement ratio of RBA caused a significant reduction of bearing capacity, while it had few effect on the hysteretic index. It was concluded that the hysteretic behavior of proposed GRBACFST column was not sensitive to the types of cementitious material and geopolymers could serve as an eco-friendly binder for concrete.

Effects of various curing methods on the compressive strength and microstructure of blast furnace slag-fly ash-based cementitious material activated by alkaline solid wastes

The large-scale stacking of alkaline industrial solid wastes such as soda residue (SR) and calcium carbide residue (CCR) has caused serious environmental problems. Therefore, a new type of cementitious material was developed in our previous study by using SR-CCR synergistically activated blast furnace slag (BFS)-fly ash (FA), which abbreviated as SCBF. This paper further studied the effects of various curing methods on the compressive strength and microstructure of SCBF, which was expected to provide guidance for its application in the field of non-reinforced products such as baking-free brick. The results show that the optimal curing scheme was heat curing at 75 °C for 12 h. The optimal scheme significantly promoted an early hydration reaction and provided the 3d/28d strength values of 16.4/24.7 MPa, exceeding those of room-temperature (RT) sealed curing and water curing by 154/24.5 % and 264/31 %, respectively. Besides, the optimal scheme accelerated the formation of CSH gel, Hydrotalcite (6MgO·Al2O3·CO2·12H2O), Hydrocalumite (3CaO·Al2O3·CaCl2·10H2O), and other crystal products, as well as increased the consolidation rate of chlorine ion from 37.9 % (in RT sealed curing) to 64.3 %. These hydration products were evenly distributed, effectively filling the pores and reducing the macroporosity from 9.30 (in RT sealed curing) to 1.54 %, thus improving the early and later-age strength. Too high curing temperature (exceeding 75 ℃) or prolong heat curing period (exceeding 12 h) would cause microstructure deterioration, significantly increase the number of macropores and microcracks in the matrix, ultimately leading to strength retrogression.

Application of molten iron desulfurization slag to replace steel slag as an alkaline component in solid waste-based cementitious materials

Desulfurization slag (DS), generated from molten iron pre-desulfurization process, has a high alkalinity that may cause seriously environmental issues. To solve the DS-disposal problem, this research proposes a new type of cementitious material composited of DS, ground granulated blast furnace slag (GGBS), steel slag (SS), and flue gas desulfurization gypsum (FGDG). The effects of DS on cementitious material were studied by testing the working performance indexes such as mortar fluidity and compressive strength, and the microscopic analysis such as XRD, TG and SEM. The results show that DS reduces the fluidity of the mortar, and significantly improves compressive strength of 3 days. The optimal ratio of DS/SS ratio in the GGBS–SS–DS–FGDG cementitious material is 1.0, and its compressive strength of 3 days and 28 days reached 24.6 and 52 MPa, respectively. The 3 days’ compressive strength of GGBS-SS-DS-FGDG is 748% higher than that of GGBS–SS–FGDG. The high alkalinity of DS promotes the dissociation of GGBS, and enhances the early hydration rate, which shortened the hydration induction period, and enhanced the cumulative released heat. Also, DS promotes the formation of ettringite (AFt) and increases the polymerization degree of the C–(A)–S–H gel at early stage. However, cementitious material containing DS has high porosity, which can be offset by the gel pores generated by SS. In summary, the GGBS–SS–DS–FGDG as a cementitious material with low carbon emission may be used to replace cement. The results of this paper can guide the large-scale and comprehensive utilization of DS with other solid waste.

Compressive strength of cemented soil in pre-bored grouted planted piles under negative temperature environment

As a new type of pile, if the pre-bored grouted planted nodular (PGPN) pile can be successfully applied to the permafrost engineering, it will have significant economic and ecological values. However, the law of strength development of cemented soil of PGPN pile under warm permafrost environment is still unclear. In this study, the strength characteristics of cemented soil were examined through unconfined compressive strength test, and factors such as the curing time at negative temperature, the types of cementitious materials, and the dosages of cement and early strength agent (ESA) were considered. The experimental results indicate thatthe cemented soil with sulpho aluminate cement (SAC) and Ordinary Portland cement (OPC) + ESA as cementitious materials show high strength and stable performance. In addition, the Reasonable dosages of the cement and ESA were suggested, respectively.

Theoretical modification of the laboratory-determined tensile stress–strain relationship of strain hardening cementitious composites (SHCCs) for large-scale specimens

Strain hardening cementitious composites (SHCCs) are a type of cementitious material reinforced with randomly distributed short fibers that exhibit tensile strain hardening behavior and prominent crack resistance. The tensile behavior of SHCCs could be significantly affected by the distribution of the fiber orientation. In large-scale specimens, the distribution of the fiber orientation is close to ideal three-dimensional uniform random distribution. However, fiber orientation distributions in laboratory SHCC specimens are influenced by the specimen dimensions (width and thickness) and casting process, resulting in neither ideal two-dimensional nor three-dimensional uniform random distribution. Therefore, the performance of large-scale SHCC specimens may be overestimated in analysis when directly using the tensile properties of SHCCs obtained from uniaxial tensile tests of small specimens. Since the uniaxial tensile tests of large-scale SHCC specimens are difficult to be conducted, theoretical evaluation of the tensile properties of mass SHCCs in large-scale specimens were conducted by modifying the uniaxial tensile test results of small specimens. In this paper, closed-form probability distribution models for fiber orientations that consider the influence of the specimen width and thickness were theoretically derived. The effects of the specimen width and thickness on the tensile properties of SHCCs were studied by applying the proposed method to the uniaxial tensile numerical model of SHCCs, while uniaxial tensile specimens with two different geometries and dimensions were tested for verification. Both the analytical and experimental results showed that, within a certain range, the width and thickness of the specimens significantly influenced their ultimate tensile strength and ultimate tensile strain. To relate the uniaxial tensile test results of laboratory-sized specimens to that of mass SHCC in large scale specimens, reduction factors for the stress–strain relationship of SHCCs obtained by traditional tensile test specimens were proposed to account for the specimen size effect based on the model analysis. The reduced tensile stress–strain relationship was applied to a finite element model of SHCC beams under four-point bending tests. It was found that the finite element analysis results obtained by using the reduced tension stress–strain relationship are in better agreement with the test results.

Enhanced mechanical properties and environmental erosion resistance with metakaolin in a kind of Chinese traditional Lime-based mortar

The Leshan Giant Buddha, which is located in Sichuan province, China, is the world’s tallest cliff statues (71 m). Due to the deterioration of the sandstone, conservation works have been carried out in past decades, and lime-based mortars have been used to repair the buddha for several times. Chuihui is a type of cementitious material used for the conservation of the Leshan Giant Buddha in 2001, but it has exhibited some deterioration due to multiple factors. In this study, metakaolin was used to enhance the volume stability, mechanical properties and environmental erosion resistance of traditional Chuihui. The results of XRD, FT-IR and Raman analyses demonstrate that metakaolin reacts with Ca(OH)2 via pozzolanic reactions and the produced C-S-H bond improves the properties of Chuihui-Metakaolin (C-M) mortars. Additionally, the microstructure of mortars becomes more compact due to the formation of cross-linked microstructures.

Local bond strength prediction of deformed reinforcing bars in concrete considering heterogeneity at interface regions

An analytical model is proposed to predict local bond strength (τf) by incorporating heterogeneity at interface regions for deformed reinforcing bars centrally anchored in concrete. The rib width on the bar surface is introduced as an interfacial characteristic parameter G in the proposed model; this accounts for the heterogeneity. Both τf and the local interfacial fracture energy (GIIf) of each specimen were found to be linked to G and can be determined analytically from the maximum pull-out loads (Fmax) from tests. It was found that the predicted τf was larger than the maximum average bond stress (τavg-max); the discrepancy between the two values reduced with an increase in L/G. Moreover, with an increase in L/G, the predicted τf showed a certain decrease, with the reduction decreasing with stronger interfacial homogeneity. The predicted GIIf was found to be significantly increased because of the weaker boundary effect. The validity of the proposed model was verified using comparisons of predicted Fmax (using the determined values of τf and GIIf) and the experimental Fmax, with the only failure mode being bar pull-out. Moreover, the model can be applied to steel or fibre-reinforced polymer bars and the concrete refers to all types of cementitious materials.

Degradation resistance of different cementitious materials to phosphoric acid attack at early stage

Sewer wastewater systems pose great threats to OPC-based concretes used for pipes due to the presence of various acids. Phosphoric acid can cause as much damage as sulphuric acid but has been very lightly studied. This study focuses on the early stage of the degradation process of different cementitious materials in phosphoric acid. Three types of cementitious materials are compared: OPC (100% cement), slag-blended OPC (slag/cement mass ratio at 65/35) and alkali-activated slag/fly ash pastes (slag/fly ash mass ratio at 50/50). Samples were exposed to phosphoric acid solution with a constant pH at 2.0 ± 0.2 for 44 days. The degradation kinetics, chemical and microstructural properties as well as dissolution rate of these binders are analysed. The results show that the alkali-activated slag/fly ash binder has the lowest degradation rate compared to the other cement-based binders. The intrinsic characteristics of the binders lead to significant changes in the kinetics of degradation. The chemical properties of the binders are the critical influential factor of the early stage behaviour. A conceptual degradation process is proposed to describe the early-stage kinetics of degradation for the cementitious materials studied.

Local bond strength prediction of deformed reinforcing bars in concrete by considering heterogeneity at interface regions

An analytical model is proposed in this paper to predict the local bond strength τf by incorporating the heterogeneity at interface regions for deformed reinforcing bars centrally anchored in concrete. The rib width on bar surface is introduced as an interfacial characteristic parameter G in the proposed model accounting for the heterogeneity. Both the τf and local interfacial fracture energy GIIf from each specimen are linked to the G and determined analytically if the maximum pull-out loads Fmax are given from the test. It is found that the predicted τf is larger than the maximum average bond stress τavg-max. The discrepancy between the two values is reduced with the increasing of L/G. Moreover, as the L/G increases, the predicted τf shows a certain decrease and the reduction becomes smaller with stronger interfacial homogeneity. The predicted GIIf is significantly increased because of the weaker boundary effect. The validity of the proposed model is verified upon the comparisons between the predicted Fmax using the determined τf and GIIf and the experimental ones with the only failure mode of bar pull-out. Moreover, the bars here can be steel or FRP (fiber-reinforced polymer) bars, and the concrete refers to all types of cementitious materials.

Reliability of chloride testing results in cementitious systems containing admixed chlorides

ABSTRACT Chloride concentrations are often evaluated for concrete mixtures used in new construction for quantity control purposes. This paper reports on the reliability of results from ASTM C1152 (acid-soluble) and ASTM C1218 (water-soluble) tests commonly adopted for measuring chlorides in concrete. The effects of cementitious material type, water-binder ratio, admixed chloride level, and degree of carbonation on chloride concentrations of cementitious systems are evaluated. Results show that the release of bound chlorides due to carbonation could be represented by an increase in ASTM C1218 test value. Chloride concentrations measured using ASTM C1152 testing could be significantly lower than the actual chloride concentration for carbonated systems. This underestimation, as a percent of total chloride concentration, could be as high as 40% depending on the cementitious material type and chloride admixed level. Preliminary results indicate that ASTM C1218 could be more reliable when compared to ASTM C1152 for systems with admixed chlorides.

Research on properties of alkali activated lead-zinc mineral powder cementitious materials

Cement has long been used as the main cementing material of the artesian paste filling material in the goaf of a mine, giving a generally high strength. However, the cement ‘two grinding and one burning’ process consumes a lot of energy, which aggravates the greenhouse effect. Therefore, a new type of cementitious material with lower energy consumption and lower emissions is needed. Solid wastes are useless by-products after mining and beneficiation, which are often dry piled in the open air, wasting land resources and polluting the environment. This project studied an alkali-activated mineral powder cementitious material, delineated its internal structure and morphology, and tested its mechanical properties. In a gelling system with 70% mineral powder, 30% Portland cement, 1% sodium silicate and a water-cement ratio of 0.4, the hydration reaction commenced the earliest and the early strength of the test block was the highest. In addition, further increasement in proportion of mineral powder or sodium silicate could not have a positive effect on the early strength of the system.

WITHDRAWN: An experimental investigation of thermocol impregnated ferrocement panel as an alternate building material

Ferrocement is a composite material and widely used for the manufacturing of aircraft hangar, boats, marine structures, light roofs etc. The application of ferrocement is numerous and due to its flexibility and durability, it gains the popularity day by day. It is a prefabricated composite and can be molded in any shape. Also, it is a flexible material and has good resistance against thermal and vibrations. Due to this ferrocement is most suitable for structures having curved surfaces such as boat, shell, domes, water tanks etc. It is cost effective and requires low maintenance. Ferrocement generally consists of thin steel wire meshes enclosed by cementitious materials. Different design of ferrocement is proposed in the past in which various layers of steel meshes and different type of cementitious materials are used. However, further improvement in its design is still going on. Sometimes in the manufacturing of ferrocement a core material which increases its resistance against impact and heat is placed. In the present research, a core material thermocol has been used in the construction of ferrocement and termed as ‘thermocol impregnated ferrocement’. The present paper describes the experimental investigation carried out to understand the behavior of thermocol impregnated ferrocement panels with different layers of meshes.