Hardened Cement Mortar Research Articles

Influence of Incorporating PVC Waste on the Mechanical Properties of Cement Mortar

Currently, recycling of industrial wastes to reduce the environmental impact is the major concerns of researchers. Polyvinyl chloride (PVC) is one of the waste materials worldwide, with considerable impacts on environmental. Recycling PVC wastes in the concrete or mortar industry is one of the adopted ways to decrease such impact. The purpose of this paper is the reuse of PVC waste deriving from the workshops manufactured doors and windows which made of PVC material. The waste of polyvinyl chloride was collected from one of the factories located in AL-Khoms, then the waste was sieved, the sample that passed through Sieve No.4 and retained on sieve No.10 was taken. The PVC waste proportions of (0.06 ˛ 0.08 ˛ 0.1) by weight of cement was added to the mix mortar. The tests carried out during this study were; air content of fresh cement mortar, flow table, dry density of hardened cement mortar, flexural and compression, free shrinkage and finally ultrasound pulse velocity. The results obtained showed a significant improvement in the sound insulation and a decrease in the dry density of the mortar. While the compressive and flexural strength results were slightly lower compared to the standard mortar. In addition, a decrease in the values of flow, free shrinkage and air content was observed with an increase in the PVC content. Nevertheless, the mortar obtained contributes to the conservation of natural resources and maintains the mechanical properties of the cement mortar in structural applications.

Novel Slow-Release Defoamers for Concrete Using Porous Nanoparticles as Carriers.

Excess large and unstable air bubbles can reduce the compressive strength of hardened concrete, and traditional defoamers always fail because of adsorption and encapsulation on cement with the progress of cement hydration in later stages. It is necessary to develop a novel defoamer that shows a sustained defoaming ability in fresh concrete. A novel slow-release defoamer for concrete using porous nanoparticles as carriers is reported for the first time. The porous nanoparticles/polyether defoamer composite (SiO2-Def) was prepared via sol-gel method. SiO2-Def is a spherical composite nanoparticle with a size range of 160-200 nm and a uniform pore size distribution. SiO2-Def shows a high load rate of about 16.4% and an excellent release under an alkali and salt environment. It has a weak initial defoaming ability but shows a sustained defoaming ability with time, so that it can avoid the failures of defoamers and eliminate harmful bubbles entrained during the processes of pumping and transportation. Moreover, SiO2-Def produced a higher compressive strength of the hardened cement mortars.

Influence of Modified Starch Admixtures on Selected Physicochemical Properties of Cement Composites.

The conducted research aimed to evaluate the influence of admixtures of various modified starches on the rheological properties of cement composites and their influence on the compressive strength of hardened cement mortars. The study involved 17 different modified starch admixtures. Using a rheometer, the values of viscosity and tangential stresses were determined depending on the shear rate, and were subsequently used to determine the yield point and plastic viscosity of cement slurries. The next parameters tested were the flow of fresh cement slurry and the compressive strength of hardened cement composite. The highest fluidisation was recorded for retentate LU-1420-0.5%Ac-R, an increase of 82%. The conducted tests led to the conclusion that admixing cement composites with modified starches changes the rheological parameters and the compressive strength of cement composites. The highest strength gains occurred for the admixtures of retentate LU-1412-R (increase of 25%). Declines in compressive strength were noticed in the retentate LU-1422-R (decrease by 13%) and the retentate OSA-2.5%-R (decrease of 17%). The admixture of starch hydrolysate significantly decreases the yield point of slurries, which in turn may contribute to the fluidisation of concrete mixes and the reduction of mixing water. The lowest values were obtained for retentates LU-1420-0.5%Ac-R (decrease of 94%), and LU-1412-R (decrease of 93%). It was found that the consistency and compressive strength of cement mortars are affected by both the type of modification and the length of the chemical chain of starch.

Both Plasticizing and Air-Entraining Effect on Cement-Based Material Porosity and Durability

The influence of a complex application of both plasticizing and air-entraining effects on concrete with polycarboxylate ether superplasticizer (PCE), air-entraining admixture (AIR), or an anti-foaming agent (AF) is analyzed in this paper with considerations for on the air content, workability, flexural and compressive strength, and freezing–thawing resistance of hardened cement mixtures. The effect of the complex behavior of PCE, AIR, and AF on the porosity of hardened cement mortar (HCM) and freezing–thawing resistance was investigated; freezing–thawing resistance prediction methodology for plasticized mortar was also evaluated. The results presented in the article demonstrate the beneficial influence of entrained air content on consistency and stability of cement mortar, closed porosity, and durability of concrete. Freezing–thawing factor KF depending on porosity parameters can be used for freezing–thawing resistance prediction. With both plasticizing (decrease in the water–cement ratio) and air-entraining effects (increase in the amount of entrained air content), the frost resistance of concrete increases, scaling decreases exponentially, and it is possible to obtain great frost resistance for cement-based material.

Synthesis and properties of different alkyl alcohol polyethers as the defoamers for concrete

In this study, we report the synthesis and properties of different alkyl alcohol polyethers as the defoamers for concrete. A series of alkyl alcohol polyethers with the same ethylene oxide unit amount (8 EO) but different alkyl chain lengths (C14~22) were obtained. The surface activities and defoaming properties of them in aqueous solutions were studied. Using them as the concrete defoamers, the defoaming properties in both fresh and hardened cement mortars were investigated, and the structure-property relationships of the polyethers were fully discussed. The results indicate that the C14 polyether showed obvious air-entraining property and the C16~22 polyethers showed effective defoaming property. As the alkyl chain length increases, the HLB value of polyether decreases (hydrophobicity increases), and the defoaming effect of polyether increases in both solutions and mortars. The results also indicate that the polyether containing longer alkyl chain length improved the mechanical performance of the hardened mortar more effectively. The study found great potential of alkyl alcohol polyethers for the practical applications as high performance defoamers.

Drying shrinkage, mechanical and transport properties of sustainable mortar with both recycled aggregate and powder from concrete waste

Utilizing recycled fine aggregate (RFA) and recycled fine powder (RFP) both from concrete waste to prepare fully recycled mortar benefits the recycling of construction waste. This investigation focused on the performance and modification of recycled mortar with both RFA and RFP, and the properties were obtained by micro- and macromeasurements. The results show that RFA contains abundant hardened cement mortar and has water absorption higher than natural aggregate, and that substituting RFP for 30% cement results in the reduction of hydration products and an increase of pore structure. Incorporating RFA increases the drying shrinkage of newly-prepared mortar, while the appropriate addition of RFP made from mortar and concrete waste reduces the drying shrinkage. Utilizing RFA and RFP are both detrimental to the mechanical strength and permeability resistance, and the performance degeneration of sustainable mortar is significant when high-volume RFA and RFP are incorporated. A linear relationship exists between the total porosity and transport properties of sustainable mortar with RFA and RFP. Substituting active mineral admixtures for a portion of RFP benefits the properties of fully recycled mortar with RFA and RFP; specifically, the addition of 10% silica fume or 10% metakaolin increases the mechanical strength by 35.9% and 38.1% and leads to decreases of 31.4% and 48.4% in the capillary absorption coefficient of fully recycled mortar, respectively. In addition, it is also beneficial for the properties of such sustainable mortar to add a mixture of RFP and recycled clay brick powder, which are both derived from construction waste.

Gamma irradiation sensitivity of early hardening cement mortar

For possible application of gamma radiation in processing of fresh concrete, like surface processing at precast plants or 3D printing, it is essential to evaluate effects of irradiation on the early hardening of cementitious binders. The influence of gamma irradiation with the dose rate of 4.6 kGy/h on the early strength, pore size distribution and qualitative phase composition of mortar was investigated. The range of investigation comprises the effects selected micro- and nano-additions to Portland cement mortar used to control the kinetic of setting and early hardening of cement. Results show that gamma irradiation of hardening mortar results in the early strength increase of about 56–100%, in reduction of capillary porosity and pore size refinement. The gamma-irradiation sensitivity of early strength of cement mortar is equivalent to increased temperature wet curing. A correlation of heat evolution characteristics of hardening mortar and the temperature-equivalent of gamma irradiation is discussed.

Effect of fly ash on the air void size distribution entrained by selected anionic, cationic and nonionic surfactants in hardened cement mortars

In this study, three types of surfactants, as anionic (mainly SDS), cationic (DTAB) and nonionic (AEO-9), were selected as the air-entraining agent (AEA). Air void size distributions of air-entrained mortars with or without fly ash were measured. The surface tension, the zeta potential of solid particles, and rheological properties were examined. The zeta potential alteration is used to characterize the interaction between surfactants and solid particles, as larger zeta potential alteration represents stronger interaction. Results indicate that the overall air-entraining behavior is governed by the surface tension, as lower surface tension leads to finer air voids. In addition, fly ash influences the air void structure by changing the interaction between surfactants and solid particles. Stronger interaction leads to finer small air voids and coarser large air voids, especially for the anionic and cationic surfactants. For the nonionic surfactant, this interaction is relatively weak, thus large air voids are affected by viscosity, as higher viscosity results in coarser large air voids.

Effect of Degree of Hydrolysis of Polyvinyl Alcohol on Adhesive Properties of Cement Mortar

Abstract Polyvinyl alcohol (PVA) is widely used in the building industry to improve the fresh and hardened properties of cement composites. In this article, the effect of partially and fully hydrolyzed PVA on physical and adhesive properties of fresh and hardened cement mortar was investigated. Results showed that both partially and fully hydrolyzed PVA could significantly improve the adhesive properties of cement mortar. The mode of rupture changed from mostly interfacial rupture without PVA in cement mortar to mixed-mode interfacial-cohesive rupture with 1.5 wt.% PVA. Partially hydrolyzed PVA-modified cement mortars had smaller bulk density and higher fluidity compared with fully hydrolyzed PVA. X-ray powder diffraction, thermal analysis, mercury intrusion porosimetry, and scanning electron microscopy were used to investigate cement hydration and microstructure of PVA-modified cement composites. As a result, fully hydrolyzed PVA was more conducive to promote cement hydration and had smaller impact on crystal structure and content of calcium hydroxide (Ca(OH)2) compared with partially hydrolyzed PVA. Besides, the addition of both partially and fully hydrolyzed PVA affected the morphology and the oriented growth of Ca(OH)2 in cement composites. Furthermore, PVA-modified mortar had finer pore size distribution and higher porosity than unmodified mortar.

Initiation of Stress Corrosion Cracking in Cold-Drawn Prestressing Steel in Hardened Cement Mortar Exposed to Chlorides

Cold-drawn, high-strength, prestressing (PS) steel strands are widely used in pretensioned concrete (PTC) structures. This paper discusses the stress corrosion cracking (SCC) of PS steel embedded in cement mortar and gradually exposed to chlorides. Various stages of the passive to active (P-to-A) transition, which marks the onset of SCC, were investigated using the electrochemical impedance spectroscopy technique. The key mechanisms were identified and confirmed using scanning electron microscopy/energy dispersive x-ray analysis, x-ray diffarction, and confocal Raman spectroscopy. It was found that the passive film on unstressed PS steel has better electrochemical characteristics than that on conventional steel rebars. However, the residual tensile stress at the surface of PS steels can assist passive film cracking after chloride attack—contrary to the pitting corrosion without cracking of passive film in conventional steels. Further, tests indicated that the concentration of chlorides required to crack the passive film in PS steels can reduce by about 50% when prestressed—as in field structures. Chemical composition, stress state, and microstructural features at the PS steel surface were identified as possible factors influencing the initiation of SCC in PTC structures.

The influence of ophiolitic crushed fine aggregate properties on the performance of cement mortars

Aggregates constitute the largest proportion of the raw materials used for the production of mortars. Therefore, their quality significantly influences the in-use performance of the aforementioned composite building materials. This paper investigates the influence of ophiolitic crushed fine aggregate, quarried in Cyprus, on the performance of cement mortars. The experimental results vividly show that the mineralogical composition and physicomechanical properties of the fine aggregate materials under study highly affect the properties of the hardened cement mortars. More specifically, cement mortars prepared with “poor quality” aggregates, exhibiting high methylene blue and Micro-Deval loss values, showed inferior physicomechanical properties, compared to composites prepared with “better quality” aggregates. Sound correlations were also found between the mineralogy of aggregates and the physicomechanical properties of the hardened composites. This suggests that the combination of standardized aggregate characterization tests and mineralogical analyses may prove useful in assessing the quality of aggregates, prior to their use in mortar production.

Effects of Gamma-Ray Irradiation on Hardened Cement Mortar

The effect of gamma-ray irradiation on cement mortar properties is investigated in this study in order to understand the mechanism behind the strength and stiffness reduction, which may be significant according to the available researches. 60Co irradiation facility with the generating dose rate of 0.1–10 Gy/s and the total activity of 4.4·1015 Bq (120 kCi) was used to perform the irradiation, so that the total observed dose of the irradiated samples reached the values ranging from 12.0 to 15.0 MGy. An identical set of control samples was placed in the same laboratory conditions away from gamma radiation. The results of nanoindentation, X-ray diffraction analysis and mercury intrusion porosimetry of the irradiated and the control samples are shown and explained in detail in this study. The nanoindentation creep compliance and the nanoindentation elastic modulus of the irradiated and the control samples do not show any significant difference. The mineral composition obtained using the X-ray diffraction analysis of the irradiated and the control samples is also similar. The pore structure rearrangement and microcrack occurrence, which were evidenced by the mercury intrusion porosimetry and scanning electron microscopy, led to the porosity increase and may be attributed to the significant decrease of compressive strength.

Discrete Element Simulation of Brittle Porous Material Failure

The study uses Particle Flow Code (PFC) 2D discrete element software to reproduce the dynamic compressive experiment of foam concrete, a typical brittle porous material, and to calibrate micro-parameters of hardened cement mortar, building a discrete element model of foam concrete. Experimental phenomena and inner mechanisms are further analyzed and studied, leading to conclusions in the deformation characterization, failure mode and failure mechanism of foam concrete specimens under different strain rate loading. The research results indicate that under low strain rate loading, the specimen cracks from inside evenly; the processes from failure to compaction is endoenergetic, resulting in stress plateau phenomenon and even deformation during the experiment. Under high strain rate loading, cracks are generated in an explosive manner at the impacted end, and the specimen on the whole is not damaged evenly. Simulation results basically fit the experiment data. The peak stress curve fitting of concrete foam from under quasi-static conditions to high strain rate is studied, which shows obvious strain rate effect that grows exponentially. By calculating models with different densities, it is found that the compressive strength of foam concrete increases along with the growth of density. Thus, PFC can be used in numerical simulation of dynamic mechanical properties of brittle porous materials.

The Use of Palm Oil Mill Effluent as Mixing and Curing Water in Cement-Based Composite

The scarcity of water, especially during the dry season, is the main factor influencing water consideration with unknown characteristics for mixing cement mortar and concrete. This study investigates Palm Oil Mill Effluent (POME) effects as mixing and curing water on the hardened cement matrix properties. The cement pastes were prepared with ordinary Portland cement, which was used as a binder. In contrast, Potable Water (PW) and POME were used separately for mixing cement and a mixture of cement and sand to produce cement paste and cement mortar, respectively. Two different mix ratios of cement: sand of 1:3 and 1:5 with the constant water-to-cement ratio of 0.5 were used to prepare the cement mortar. The PW and POME were also utilized as the liquid curing media for hardened cement mortar until the testing ages of 7, 14, and 28 days. Soundness, normal consistency, and setting times tests were performed to evaluate cement paste’s fresh properties, while unit weight and compressive strength tests to determine the hardened properties of cement mortar at different ages. The results showed that soundness, normal consistency, and setting times of cement paste with POME as mixing water were higher than that of PW. This indicates that POME exhibits the potential of serving as retarding admixture. The unit weights of mortar (1:3 or 1:5 mix proportion) with POME as mixing water were lower than those produced with PW as mixing water after curing in PW or POME for 28 days; but for the mortar with POME as mixing water, the unit weight was slightly higher when cured in POME than water at the same curing age. The mortar specimens with 1:3 mix proportions with PW as mixing and curing water had the maximum 28-day compressive strength values of 26.01 N/mm2, while a decrease of 20% was recorded when cured in POME. Further decrease in 28-day compressive strength values was recorded cement mortar with 1:3 mix proportions and POME as mixing water after being cured in PW and POME. A similar trend was observed for cement mortar with 1:5 mix proportion with POME as mixing water when cured in PW and POME, and PW as mixing water when cured in POME, compared with the cement mortar with PW when cured in PW for 28 days. The maximum strength reduction of 20% specified by the standard for cement composite or concrete at 28 days of curing for water from the questionable source was exceeded with the use of POME as mixing water. It can be concluded that POME is not suitable for mixing cement mortar.

Effects of polycarboxylate superplasticisers with various functional groups on the pore structure of cement mortar

The air-entraining capabilities of polycarboxylate superplasticisers (PCEs) with different functional groups were systematically analysed. Using different molecular PCEs, the evolution process from bubbles in fresh cement mortar to pores in hardened cement mortar was investigated, considering their effects on mortar workability and mechanical performance. The results showed that PCEs with various functional groups have different air-entraining capabilities. PCEs with ester groups decreased the surface tension and significantly promoted the air-entraining capability, resulting in a notable increase of air content in fresh cement mortar. PCEs with sulfonic acid groups increased the surface tension and remarkably decreased the air content in the fresh cement mortar. A higher air-entraining capability benefits the dispersing properties of PCEs and therefore the PCEs with ester groups performed better in dispersibility in comparison with the PCEs with sulfonic acid groups. The stability of bubbles entrained in fresh cement mortar leads to differences in the pore structure of hardened cement mortar. The PCEs with ester groups diminished the size of large bubbles, leading to significantly decreased porosity of the hardened mortar. PCEs with sulfonic acid groups in the backbone barely optimised the pore structure, with a large amount of large pores remaining in the hardened mortar. Decreased porosity and pore size hence led to higher compressive strength of the hardened cement mortar.

Influence of sulphate ions on the crystal chemistry of white cement mortars with a high content of marble filler powder

Objects of this research are white cement mortars, characterized by both of high content of addition of marble powder and reduced water-cement ratio. The hardened cement mortars, formed after 28-and 120-day curing under standard conditions, are studied. The newly formed phases, containing [SO4]2-, [CO3]2-, [OH]-, etc., are identified using X-ray powder diffraction, infrared spectroscopy and thermal analysis (coupled with analysis of the outgoing gas mixture by mass spectrometry). Based on of the formed calcium silicate hydrates, calcium aluminate hydrates, the influence of sulphate ions is analysed and the mechanism of the thermal decomposition reaction at high temperatures in an oxidizing gas environment is studied. This allows us to establish that the hydration of Portland cement depends on the addition of marble powder (technically calcium carbonate CaCO3), as well as mono- and hemicarboaluminates are formed instead of monosulphoaluminates.

Mesoscopic numerical simulation of fracture process and failure mechanism of cement mortar

AbstractCement mortar is an important part of building material and a typical cement matrix composite material. In current work, the mechanical properties and failure mechanism of cement mortar under static compression are studied by using the Base Force Element Method (BFEM). The static compression damage program of cement mortar is compiled grounded on the BFEM of the potential energy principle. An elastic polyline damage constitutive model is put forward to express the meso‐damage and evolution process of cement mortar. A 2D random circular aggregate model of cement mortar was established. The numerical simulation of the uniaxial static compression is carried out, the stress–strain curve, damage process, and damage model are obtained. The strength of the interfacial transition zone and the failure process of hardened cement mortar were discussed. A mesoscopic equivalent model is proposed to analyze the mechanical properties of cement mortar by considering the effect of initial porosity.

Carbonation study and determination of cement to sand ratio in hardened cement mortar by X‐ray photoelectron spectroscopy

The determination of cement and sand content in an aged cement mortar is a challenging problem for civil engineers. Techniques like x‐ray diffraction (XRD), thermogravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS) are well established, which can give some insight of the hydrated products. The present study is an attempt to use x‐ray photoelectron spectroscopy (XPS) technique for the evaluation of ordinary Portland cement (OPC), sand (aggregate) composition and carbonation study in hardened cement mortar. Carbonation analysis and cement to sand ratio for all mortar compositions has been determined and studied in detail in the present work. The C 1s spectra of cement mortar with ratios 1:1, 1:3 and 1:6 shows carbonate formation on the surface with 21, 40 and 32 atomic percent, respectively. An increase in SiO2 content corresponding to sand is observed for all three mortar mix. The formation of silica gel due to carbonation has not been observed in the mortar samples. The cement to sand ratio for all three mortar mixes is found to be in 20–30 percent error limit due to the heterogeneous nature of the mortar system.

Assessment of waste hardened cement mortar utilization as an alternative sorbent to remove SO2 in flue gas

Developing efficient low-cost absorbents has been recognized as a prerequisite for industrial application of wet flue gas desulfurization (WFGD). Herein, hardened cement mortar (HCM) particles developed from waste concrete blocks were used as an innovative absorbent for SO2. The results show that the SO2 in flue gas can be completely absorbed by the highly alkaline HCM slurry. Under optimum operating conditions, 0.8 g of SO2 was retained by per gram of HCM. Under acid conditions produced upon dissolving SO2 in water, the Ca-rich compounds in HCM particles can continuously release Ca2+ and OH− into the HCM slurry. The Ca2+ ions released can effectively combine with SO32−, resulting in the absorption of SO2 dissolved in water. The dissolution process of HCM particles is well described by the pseudo-second-order model. The desulphurization byproduct was characterized by X-Ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and energy dispersive spectrometry (EDS). The results show that the desulphurization product mainly consists of gypsum. The technology developed provides a type of new material for removing SO2 in waste flue gas. It also offers an innovative solution for the disposal of waste concrete which is also a global environmental concern.

Mechanical Properties and Microscopic Mechanism of Coral Sand‐Cement Mortar

The workability and mechanical performance of coral sand‐cement mortar (coral mortar, for short) and the modification effects of mineral admixtures on the coral mortar were studied in this paper. The results showed that the strength of coral mortar was lower than that of standard mortar, but the strength of coral mortar was improved by compositing with the mineral admixture, which can be attributed to the improvement of the microstructure and interface transition area. Scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to explore the microscopic mechanism involved in the mechanical properties, volume stability, and hydration of mortar. The analyses revealed that the internal curing effect of coral sand improved the mechanical properties of mortar and its ability to resist shrinkage. The uneven surface of coral sand formed a meshing state of close combination with the hardened cement mortar, which helped to improve the volume stability of mortar. The Ca2+ and Mg2+ ions from coral sand participated in the hydration reaction of cement, which contributed to generating more hydration products. Moreover, the microaggregate filling and pozzolanic effects of fly ash and slag improved the mechanical properties of coral mortar and resistance to chloride ion diffusion.