Influence of polymers on microstructure and adhesive strength of cementitious tile adhesive mortars

The impact of polymer modification on the physical properties of cementitious mortars is investigated using a multimethod approach. Special emphasis is put on the identification and quantification of different polymer components within the cementitious matrix. With respect to thin-bed applications, particularly tile adhesives, the spatial distributions of latex, cellulose ether (CE), polyvinyl alcohol (PVA), and cement hydration products can be quantified. It is shown that capillary forces and evaporation induce water fluxes in the interconnected part of the pore system, which transport CE, PVA, and cement ions to the mortar interfaces. In contrast, the distribution of latex remains homogeneous. In combination with results from qualitative experiments, the quantitative findings allow reconstruction of the evolution from fresh to hardened mortar, including polymer film formation, cement hydration, and water migration. The resulting microstructure and the failure modes can be correlated with the final adhesive strength of the tile adhesive. The results demonstrate that skinning prior to tile inlaying can strongly reduce wetting properties of the fresh mortar and lower final adhesive strength.     

Evaluation of various cellulose ethers performance in ceramic tile adhesive mortars

Eleven cellulose ethers (CE) were selected and tested in a cement based ceramic tile adhesive (CTA) formulation designed to highlight the effect of the CE on the end-use values of the mortars. Results showed that the end-use values, either in the fresh or hardened state, are strongly influenced by the latex powder/CE choice. This is due to the competitive adsorption between these two components; in the fresh state, it affects the CE concentration in the pore solution and hence the viscosity of the mortar, setting time, and skinning. In the hardened state, when CE films do not prevent evaporation at the tile–mortar interface, adhesion in hot curing conditions is lowered compared to dry tensile adhesion values. Test results showed that CTA formulations should be thought of in terms of the CE/latex powder couple, since interactions between this couple and the cement, strongly influence end-use values of the mortar.     

可再分散乳胶粉对瓷砖胶性能的影响

通过添加不同类型的可再分散乳胶粉及聚乙烯醇（PVA）粉末，并按照不同的比例制成瓷砖胶。瓷砖胶在室温养护、热养护和水养护等条件下成型，并按照JC／T547-2005、JG149—2003标准对其相关性能进行测定。结果表明，含有特殊组分的三元共聚可再分散乳胶粉对瓷砖胶的制备较适合。     

Influence of mix proportions on microstructure and gas permeability of cement pastes and mortars

This paper presents a study on the influence of mix proportions of cementitious materials on their transfer properties, namely porosity and gas permeability. These latter are known as durability indicators. The work is performed on a wide range of cement pastes and mortars (24 compositions). These compositions are defined by mix proportion parameters (water/cement ratio, limestone filler/cement ratio, and amount of superplasticizer and volume fraction of paste). To characterize these materials, an experimental campaign was carried out, including different types of test (water porosimetry, mercury intrusion porosimetry, desorption isotherms and gas permeability). The influence of the composition parameters on the studied durability indicators is highlighted and correlation between gas permeability and microstructural properties (total porosity and critical pore diameter) is established. Finally, a method to predict materials permeability from that of the cement paste is proposed.     

Autogenous and drying shrinkage of alkali-activated slag mortars

Shrinkage of alkali-activated slag (AAS) cement is a critical issue for its industrial application. This study investigated the mechanisms and effectiveness of shrinkage-reducing agent (SRA) and magnesia expansive agent on reducing autogenous and drying shrinkage of AAS mortars that were activated by liquid sodium silicate (LSS) solution with modulus (SiO₂/Na₂O molar ratio) of 0-1.5. The results showed that the autogenous shrinkage of AAS mortars increased with the increase of LSS modulus from 0 to 0.5, then decreased as modulus increased up to 1.5. The drying shrinkage consistently increased with the increase in the modulus of LSS. The oxyalkylene alcohol-based SRA could significantly reduce the autogenous and drying shrinkage of AAS mortars while the magnesia expensive agent was comparatively less effective. The autogenous shrinkage of AAS mortars was inversely proportional to the internal relative humidity, while the drying shrinkage was more related to the mass loss of samples. Mathematical models were established to describe the autogenous and drying shrinkage behavior of AAS mortars.     

Link between microstructure and tritiated water diffusivity in mortars: Impact of aggregates

The present study aims to investigate the influence of microstructure, particularly the effect of aggregates content and interfacial transition zone (ITZ), on tritiated water (HTO) diffusivity in mortars.To this end, three different series of mortars were prepared and HTO diffusion tests were conducted. Variables are water-to-cement ratio, sand volume fractions, and particle size distribution. In parallel, the microstructure of these materials was characterized by water porosimetry, mercury porosimetry, and by backscattered electron microscopy associated to images analysis.It was observed that at low sand content (0%–50%), diffusion properties of mortars are dominated by aggregates dilution effect. Beyond 50% of standard sand, other effects related to the large number of sand grains appear, such as air voids and porous areas mainly due to the difficulty of obtaining well-compacted materials.     

Plastic shrinkage of mortars with shrinkage reducing admixture and lightweight aggregates studied by neutron tomography

Water transport in fresh, highly permeable concrete and rapid water evaporation from the concrete surface during the first few hours after placement are the key parameters influencing plastic shrinkage cracking. In this work, neutron tomography was used to determine both the water loss from the concrete surface due to evaporation and the redistribution of fluid that occurs in fresh mortars exposed to external drying. In addition to the reference mortar with a water to cement ratio (w/c) of 0.30, a mortar with the addition of pre-wetted lightweight aggregates (LWA) and a mortar with a shrinkage reducing admixture (SRA) were tested. The addition of SRA reduced the evaporation rate from the mortar at the initial stages of drying and reduced the total water loss. The pre-wetted LWA released a large part of the absorbed water as a consequence of capillary pressure developing in the fresh mortar due to evaporation.     

Quantifying the effects of crack width,tortuosity, and roughness on water permeability of cracked mortars

The existing service-life prediction models rarely account for the effect of cracks on mass transport and durability of concrete. To correct this deficiency, transport in fractured porous media must be studied. The objective of this paper is to quantify the water permeability of localized cracks as a function of crack geometry (i.e., width, tortuosity, and surface roughness). Plain and fiber-reinforced mortar disk specimens were cracked by splitting tension; and the crack profile was digitized by image analysis and translated into crack geometric properties. Crack permeability was measured using a Darcian flow-thru cell. The results show that permeability is a function of crack width square. Crack tortuosity and roughness reduce the permeability by a factor of 4 to 6 below what is predicted by the theory for smooth parallel plate cracks. Although tortuosity and roughness exhibit fractal behavior, their proper measurement is possible and results in correct estimation of crack permeability.     

Influence of microstructure on oxygen transport in perovskite type membranes

Abstract

The influence of bulk microstructure (grain size distribution, grain boundary length) on the oxygen transport properties of permeation membranes has been investigated. For this purpose, La_0.5Sr_0.5FeO_3-δ samples with different microstructures were prepared by varying sintering time and temperature. Average grain sizes, which ranged from 0.20 to 1.43 μm, were determined by SEM analysis. The oxygen transport properties of the samples were characterised by permeation measurements as a function of temperature in an air/argon oxygen partial pressure gradient. The fluxes presented a change in activation energy, which was attributed to a change in the rate limiting step, from bulk diffusion at lower temperature (< 850°C) to surface limitation at higher temperature (> 900°C). Only transport through the bulk was influenced by the microstructure, with the highest flux for the smallest grains. At 800°C, the fluxes were respectively 0.06, 0.03 and 0.01 μmol cm^-2 s^-1 through ≈ 1 mm thick samples with average grain sizes of 0.20, 0.63 and 1.43 μm respectively. This would imply that oxygen transport occurs more rapidly along grain boundaries than through the bulk. Grain boundary structure and composition were analysed by TEM.     

Drying and autogenous shrinkage of pastes and mortars with activated slag cement

Activated slag cement (ASC) shows significantly higher shrinkage than ordinary Portland cement agglomerates. Cracking generated by shrinkage is one of the most critical drawbacks for broader applications of this promising alternative binder. This article investigates the relationship between ASC hydration, unrestrained drying and autogenous shrinkage of mortar specimens. The chemical and microstructure evolution due to hydration were determined on pastes by thermogravimetric analysis, conduction calorimetry and mercury porosimetry. Samples were prepared with ground blast furnace slag (BFS) activated with sodium silicate (silica modulus of 1.7) with 2.5, 3.5 and 4.5% of Na₂O, by slag mass. The amount of activator is the primary influence on drying and autogenous shrinkage, and early hydration makes a considerable contribution to the total result, which increases with the amount of silica. Drying shrinkage occurred in two stages, the first caused by extensive water loss when the samples were exposed to the environment, and the second was associated with the hydration process and less water loss. Due to the refinement of ASC porous system, autogenous shrinkage is responsible for a significant amount of the total shrinkage.     

可再分散乳胶粉对瓷砖胶性能的影响研究

通过添加不同类型的可再分散乳胶粉及聚乙烯醇(PVA)粉末,并按照不同的比例制成瓷砖胶。瓷砖胶在室温养护、热养护和水养护等条件下成型,并按照JC/T547-2005、JG149-2003标准对瓷砖胶的相关性能进行测定。结果表明:采用含有特殊组分的三元共聚可再分散乳胶粉,对瓷砖胶的制备较适合。     

Influence of the kneading water content in the behaviour of single-coat mortars

The effect of water content in the kneading process of mortars for application as single-coat renders was evaluated in terms of several properties. These properties refer to the mortar product in the fresh and hardened state. Characteristics under evaluation in function of kneading water are, for fresh mortar, the apparent density and entrained air while, for hardened products, apparent density, shrinkage, mechanical properties, abrasion wear and permeability amongst others. If some of these characteristics are obtained by standard tests, others, like abrasion wear, had to be adapted and are described here.Both for fresh and hardened products characteristics, kneading water amount significantly changes them and it was possible to establish the proper content of water to be used in order to get a well-behaved single-coat mortar.     

陶瓷墙砖胶失效模型研究及其风险评估

通过国内监督抽查信息提炼和市场样品采集检测,分析了陶瓷墙砖胶使用过程中存在的风险因素;通过人工加速老化试验及失效模型构建,采用风险评估模型判定了其风险大小。研究结果表明:国内现阶段陶瓷墙砖胶的合格率仅为84.62%;热老化是相对最大的风险因素,能迅速导致胶粘剂的胶接强度下降,部分陶瓷墙砖胶的胶接强度衰减率超过90%(失效情况明显);陶瓷墙砖胶存在中等安全风险。     

Effect of geothermal waste on strength and microstructure of alkali-activated slag cement mortars

Mortars of blast furnace slag replaced with 10% of a geothermal silica waste were cured for 90 days. The binder was activated by 6 wt.% Na₂O equivalent of NaOH and water glass. The presence of the silica enhanced the formation of hydration products as shown by nonevaporable water (NEW) results. Backscattered electron images indicated that the microstructures of blended slag had less porosity than those of neat slag mortars and the interfacial zone between aggregate and hydration products was dense and of homogeneous composition similar to the matrix of hydration products. The main hydration products were C-S-H and for NaOH a hydrotalcite type phase was found as finely intermixed with the C-S-H.     

粉煤灰改性瓷砖背胶性能研究

研究了粉煤灰改性瓷砖背胶在不同龄期、环境条件下的拉伸粘接强度。研究结果表明:粉煤灰的加入可很好地改善瓷砖背胶耐水、冻融和热老化性能;但改性后的瓷砖背胶在浸水及冻融条件下较标准养护条件下的拉伸粘接强度有所下降,热老化条件下的拉伸粘接强度明显提高,且各环境条件下瓷砖背胶的拉伸粘接强度随着龄期的增长而减小。通过SEM(扫描电镜)分析,粉煤灰的加入使得瓷砖背胶固化后絮状生成物明显增多,尤其在热老化条件下界面处形成更为致密的网状结构;但浸水及冻融条件下聚合物膜发生溶胀和冻胀,界面结构较标准养护条件下疏松,导致拉伸粘接强度下降。     

瓷砖背胶的应用力学性能研究

介绍了瓷砖背胶的应用特点及其粘接强度的检测方法。采用实验室检测方法测得了AT-701S(自制瓷砖背胶)和市售同类产品的相关性能。研究结果表明:AT-701S的相关性能接近甚至超过市售同类产品;AT-701S的浸水粘接强度(大于0.7 MPa)低于室温粘接强度(1.0 MPa),热储存粘接强度(1.3 MPa)明显提高,冻融循环粘接强度(0.88 MPa)与浸水粘接强度相近;AT-701S施工简单、造价低且性能满足应用要求。     

Combined effect of expansive and shrinkage reducing admixtures to obtain stable and durable mortars

In order to improve the dimensional stability of cement based mortars, the effects produced on cement hydration of a shrinkage reducer (propyleneglycol ether based—SRA) and an expansive admixture (calcium oxide based—EXP) were investigated. Mortar samples (prepared without admixtures or with SRA or EXP or SRA and EXP) were compared through compressive strength measurements, water evaporation, restrained shrinkage and restrained expansion measurements. Setting time and free expansion were also detected on cement paste specimens.

A synergistic effect on the shrinkage reduction was observed when the shrinkage reducing admixture and the expansive agent were used together. In order to clarify this phenomenon, the hydration of cement pastes containing these kinds of admixtures was followed by ESEM-FEG (environmental scanning electron microscopy–field emission gun), TG (thermogravimetry), specific surface area measurements (by BET—Brunauer–Emmet–Teller-method) and XRDS (X-ray diffraction spectroscopy).     

Porous single-fired wall tile bodies: Influence of quartz particle size on tile properties

This study examines the effect of quartz particle size in raw material composition customarily used for the manufacture of porous single-fired wall tile bodies on the characteristics of the green tiles and on the thermal and mechanical properties of the fired tiles. Quartz particle size was varied, while the quantity and particle size of the other raw materials were kept constant. Tile compacts were formed by uniaxial pressing and fired at different peak temperatures. The resulting fired microstructure was then characterised and tile thermal and mechanical properties were determined. Microcrack formation around quartz particles leads to hysteresis of the coefficient of thermal expansion during heating and cooling. The studied mechanical and thermal properties are shown to be a function of the magnitude of the hysteresis and porosity. This relationship is independent of the operating variables (pressing pressure, operating temperature, and quartz particle size) used. The results obtained confirm that the green and fired properties of porous single-fired wall tiles may be considerably enhanced, while holding low shrinkage and high porosity, compatible with low moisture expansion, by reducing quartz particle size and appropriately adjusting the pressing pressure and peak firing temperature. This should enable thin and/or large-sized porous wall tiles to be manufactured, without (immediate or delayed) curvatures, and with a higher breaking load than that required by the standards.     

Influence of hydroxypropylguars on rheological behavior of cement-based mortars

Hydroxypropylguars (HPGs) are used as water retention agents in modern factory-made mortars. Nevertheless, these molecules can also impact the rheological behavior of cement-based materials. The influence of HPG and its dosage on mortar rheological properties was thus investigated thanks to a suitable measurement procedure. HPG allows keeping a positive yield stress value while the yield stress of hydroxypropyl methyl cellulose (HPMC) mortars was found to decrease with an increase in dosage. HPG increases the shear-thinning behavior and the consistency of mortars. The study of pore solution viscosity suggests that the entanglement of HPG coils beyond a threshold dosage is crucial to understand the rheological macroscopic behavior of HPG-admixed mortars. Nevertheless, the increase in mortar viscosity induced by HPG was lower than expected which reveals additional and specific repulsive forces induced by polysaccharides.