Mechanical and adhesion properties of polymer-modified cement mortars in relation with their microstructure

In this study, cement mortars were modified with a commercial polymer admixture. The aim of this study is to investigate the influence of the polymer content on the mechanical and adhesion properties of the mortars and to relate these properties with mortars’ microstructure. A series of mortars were produced with various polymer/cement/water/aggregate ratios. The adhesion properties of the mortars to clay bricks were tested with a simplified tensile testing measurement. The microstructure of mortars, as well as interfaces, were evaluated by Scanning Electron Microscopy (SEM). It was found that with high polymer content, large size hardened particles are formed, reducing the compressive strength of the mortars. Polymer addition enhances the adhesion between the mortar and brick. The mortar microstructure at the interface affects the adhesion properties and the mode of failure.     

Characteristics of brick used as aggregate in historic brick-lime mortars and plasters

Mortars and plasters composed of a mixture of brick powder and lime have been used since ancient times due to their hydraulic properties. In this study, raw material compositions, basic physical, mineralogical, microstructural and hydraulic properties of some historic Ottoman Bath brick-lime mortars and plasters were determined by XRD, SEM-EDS, AFM, TGA and chemical analyses. The mineralogical and chemical compositions, microstructures, morphologies and pozzolanicities of the brick powders and fragments used as aggregates in the mortars and plasters were examined to find out the relationship between hydraulic properties of the mortars and the bricks. The characteristics of bricks used in the bath domes were also determined to investigate whether the brick aggregates used in mortar and plasters were prepared from these bricks. The results indicated that the mortars and plasters were hydraulic owing to the presence of crushed brick powders that have good pozzolanicity. The brick powders had high pozzolanicity because they contained high amounts of calcium-poor clay minerals in their raw materials that were fired at low temperatures. On the other hand, bricks used in the domes had poor pozzolanicity with different mineralogical and chemical compositions from bricks used in mortars and plasters. Based on the results of the analysis, it was thought that the bricks manufactured with high amounts of clays were consciously chosen in the preparation of hydraulic mortars and plasters.     

Investigation of Shale Brick Interface with Cement-Lime and Polymer-Modified Mortars

Bonds between cement-lime mortar and shale brick, and between polymer-modified mortar and shale brick, were studied using a scanning electron microscope (SEM). The results showed that the bond is greatly influenced by the microstructure and chemical composition of the mortar at the interface contact area and by the microstructure of the brick surfaces. For relatively porous bricks, cement-lime mortars give a better bond, apparently due to better interpenetration of the fresh mortar into the open pores of the brick, creating a greater bond area. The presence of calcium contributes to good bonds, while large amounts of silicon were found in poorly bonded areas. Latex-modified mortars are not able to penetrate brick surfaces and are able to create strong bonds only on limited locations and allow water to enter brick masonary.     

北京延庆和怀柔明代长城灰浆微结构剖析对比研究

长城是世界文化遗产,长城灰浆是其保护修缮中的关键材料。本研究通过X射线荧光光谱分析、X射线衍射分析、热重分析、场发射扫描电镜、傅里叶红外光谱分析等对延庆及怀柔地区长城砌筑灰浆以及延庆长城不同部位灰浆的成分组成、晶体结构、微观形貌等进行系统剖析。结果表明,延庆和怀柔地区长城砌筑灰浆成分差异较大,怀柔灰浆中Mg、Si和有机物含量远高于延庆灰浆,这是由于怀柔灰浆石材原料中可能含有较多的菱镁矿,而且怀柔灰浆中含有少量的砂子。两地砌筑灰浆中均含有糯米,糯米使CaCO₃晶粒尺寸变小,结构更致密。同一地区不同部位和用途的灰浆组成也存在差异:灌浆灰浆与其他种类的灰浆差异较大,含有较多的砂子和石子,石缝灰浆中含有少量的细砂;路面砌筑灰浆碳化不充分,含有少量的Mg(OH)₂和Ca(OH)₂;砖砌筑、勾缝、路面砌筑灰浆中检测到糯米的存在,灌浆和石缝灰浆中未检测到糯米。本研究将为长城修复灰浆的配制提供理论依据。     

VOLUME CHANGES IN BRICK MASONRY MATERIALS1

Volume changes in brick and mortars attending variations in moisture content and temperature have been studied. There were included in the study 21 cements (both Portland and masonry), 7 limes, and 8 makes of brick received from various sections of the United States. The shrinkage of mortars during hardening and the alternate expansion on wetting and shrinkage on drying occurring subsequent to hardening have been measured. Varying the moisture content produced far smaller volume changes in well-fired brick than in most of the mortars. Underfired brick expanded appreciably on wetting. It is indicated that differential volume changes between brick and mortar caused by variations in moisture content are apt to be greater than those produced by normal temperature variations. Volume changes in hardened mortars were least in the case of straight lime-sand mortars.     

Post-mortem analysis of MgO–Al2O3–C bricks containing bauxite used in steel ladle walls

A serious problem with integrated masonry linings ladle was that the ladle wall bricks were difficult to be partially replaced. Thus, the service life of the ladle was determined by the properties of ladle wall bricks. In this study, the new generation of MgO–Al₂O₃–C bricks with bauxite aggregates was tested in a ladle lining of an integrated steel ladle for 103 cycles, and the corroded microstructure of the used brick was investigated. A multilayered structure of bauxite aggregates could be observed in the used brick, which inhibited the slag penetration along the boundary of the magnesia aggregates and reduced the degree of the aggregates fall off from the used bricks. Besides, during the process of slag penetration, bauxite aggregates could melt into the slag, which increased the viscosity of the slag and weakened the penetration ability of the slag. The MgO–Al₂O₃–C bricks with bauxite addition could improve the service life of the ladle to a certain extent.     

WATER-TIGHT TERRA COTTA MASONRY*

In spite of the lessened opportunity for moisture to pass the face of a terra cotta wall as compared with brick masonry, certain precautions should be observed to produce a water-tight wall, especially where the exposure is severe. The bearing of each of the important properties of masonry cements in regard to their application to terra cotta is pointed out and recommendations are made for suitable cementing materials. Suggestions are offered for the selection of sand and for securing uniformity and intimacy of mix. A joint width of to ¼ inch is recommended where the regularity Of the units permits. The joints should be shoved and given a tool finish at the proper stage of stiffening. The joints subjected to extra severe exposure should be packed with prehydrated mortar and properly tool-finished. Mortar may be aided to adhere to a glazed surface either by using prehydrated mortars or by first painting the surfaces with cement paint. For back-up, a hollow tile with webs vertical is recommended.     

TESTS OF REINFORCED BRICK COLUMNS*

This paper presents the data obtained in an extensive investigation on reinforced brick columns. The results furnished a basis for the development of rational design formulas. The strengths of the columns were found to be made up of the effective strength of the masonry plus the yield-point strength of the longitudinal reinforcement. A study of the type of masonry mortars revealed the fact that Portland cement mortar containing 15% ordinary brick clay by weight of the cement gave better results than did any of the other types used. A review of all known experiments on brick piers and columns is given.     

Effect of natural pozzolana and polypropylene fibers on the performance of lime mortar for old buildings restoration

The main objective of this research is to elaborate a mortar based on lime (L), pozzolana (PZ) and polypropylene fibers (PP) to restore and renovate the stone constructions while maintaining their initial comfort. Unlike the new buildings, in rehabilitation, we have to deal with the existing ones. For this purpose, mortars samples from an old building, chosen as cases of study, were taken and chemically analyzed in order to reproduce their equivalent mortars. Three different mortars were made and studied. A lime based mortar (M1), lime-pozzolana based mortar (M2) and lime-pozzolana based mortar with polypropylene fibers (M3). In order to preserve the thermal comfort offered by the old building, the thermal conductivity and the mechanical proprieties were studied. The adhesion of each mortar was also tested on several support types (concrete, concrete block, brick and natural stone). Finally, the three studied mortars were applied on the facade of the chosen building. The results are satisfactory on both levels aesthetic and adhesion. The incorporation of polypropylene fibers was more promising regarding thermal comfort. Moreover, their use lightened the matrix and improved the tensile strength.     

CONSTRUCTION OF WATER-TIGHT BRICK MASONRY1

About 300 panels have been erected to determine the effect of some of the various factors of different brick, mortars, workmanship. and design in causing leaky brick walls. The brick varied in absorption from 0.6 to over 12% of their weight when placed flat side down in 1/8 inch water for ten minutes. The mortars included both lean and the richest mixes of lime and Portland cement in varying proportions and of a large number of masonry cements. Most of the panels one brick in thickness leaked in half an hour on being sprayed with a hose. A very few mortars were found that were quite tight. Those panels with an air space between the front and the backing allowed no water to pass clear through the wall. Many panels have been broken in flexure with very interesting and important results. Other panels have been built to test out interior ventilation of walls, and many other points have been studied.     

Effect of binding system on the compressive behaviour of refractory mortars

In refractory masonry lining of industrial furnaces the compressibility of mortars is critical for the thermo-mechanical integrity of the structure. Compressive stress–strain behaviour of refractory mortars has been measured during drying at room temperature and in the service temperature range of 300–1400 °C. The results have been explained using fractographic analysis and distinct element method computer modelling. The mortar failure has been shown to occur due to formation of shear bands of micro-cracks. The propagation of cracks preferably follows the shortest path between larger pores and is influenced by grain cohesion and interlocking. Tests with mortars featuring calcium aluminate cement, mono aluminium phosphate, water glass and bentonite clay binders have indicated that besides increasing the cohesion between the grains the binder reduces the internal friction that promotes higher compressibility. It has been found that the mortar with clay has the highest compressibility. The mortar with cement shows the most stable behaviour.     

Influence of the Ca/Si ratio of the C–S–H phase on the interaction with sulfate ions and its impact on the ettringite crystallization pressure

The effect of the Ca/Si ratio of the calcium–silicate–hydrate (C–S–H) phase on the interaction with sulfate ions is investigated for C–S–H phases (Ca/Si = 0.83, 1.25, 1.50) and mortar samples of blended Portland cements. It is shown that leaching of calcium from C–S–H and portlandite affects the composition of the pore solution and contributes to the developing crystallization pressure of ettringite. Sulfate profiles show that sulfate binding before cracking is similar for different Ca/Si ratios whereas the highest expansion rates are observed for the mortars with the highest Ca/Si ratios. After leaching in sulfate solutions, the C–S–H samples have been characterized by ²⁹Si MAS NMR, thermogravimetric analysis, and elemental solution analysis. Generally, the exposure to sulfate solutions results in decalcification of the C–S–H, which increases with decreasing Ca/Si ratio. The data are in good agreement with thermodynamic modeling, indicating that equilibrium is almost achieved in the leached systems. Finally, the expansion of mortar samples exposed to sulfate solutions was much less at lower Ca/Si ratios of the cement blends. This reduced expansion can be related to the decrease of the supersaturation of the pore solution with respect to ettringite at lower Ca/Si ratios of the C–S–H and in the absence of portlandite.     

Effect of epoxy resin on the intrinsic properties of masonry mortars

The paper presents an assessment on the properties of three different types of masonry mortars, namely Portland cement mortar (CM), polymer cement mortar (PCM) and polymer mortar (PM) of various compositions. The effect of binder content (cement and/or epoxy) on CM, PCM or PM has been explored in the study. An assessment was carried out on the basis of mechanical (compressive, tensile and flexural strength), physical (water uptake, chloride ion permeability), morphological (porosity) and thermal (coefficient of thermal expansion) properties of the mortars. A comparative cost analysis of the mortars is also discussed in this article. The results show that the mechanical strength of both PCM and PM improves markedly with the addition of epoxy resin, and the higher rate of incremental strength is found for PM. Consequently, the chloride ion penetration, water uptake, porosity and thermal expansion of the mortars decrease significantly with the resin content, but the rate of drop in chloride ion penetration, water uptake, porosity and thermal expansion is much higher for PM. The test results indicate that the variation of binder content (epoxy/cement) is found to be the key factor determining the mortar properties and cost.     

A study of the adhesion between hydraulic mortars and concrete

Knowledge of the adhesion properties of materials is necessary for many applications. When one has to cover a wall or a concrete pavement with mortar, it is necessary to pay attention to the adhesion between the two materials, otherwise one can have some problems such as the delamination of the two materials after application. We present here a study of the adhesion between hydraulic mortars and concrete. Mortars with permeability-reducing admixtures were used. This type of mortar is used to reduce the possibility of water infiltration in construction. Mortars should be impermeable but this should not affect the adhesion. To measure the adhesion, we used the pull-off test. The results show a decrease in the adhesion strength with increasing permeability-reducing admixture dosage, except for one of the admixtures used. We believe that this result is a consequence of the decrease in porosity caused by the use of a more waterproofing admixture and that a higher dosage contributes to the increase of admixture at the interface. To confirm this, we performed a microscopic analysis of the failure surfaces of the mortars. The decrease in porosity was well seen in this analysis. However, this characteristic of mortars is not the only one that affects adhesion. The composition of the admixture is very important as we found different adhesion strengths, for similar porosity, with different admixtures.     

Latex influence on the mechanical behavior and durability of cementitious materials

The results of an experimental program conducted on latex-modified mortars are presented in this article. These mortars have become of growing interest in the field of construction. They were used as superplasticizers, or water reducers, for finishing work applications and for repairs, coatings, and waterproofing. This study is about using two polymers (latex), i.e. styrene–butadiene rubber and styrene–acrylic, in order to assess their performance in replacing cement in mortars. A series of mortar mixtures, containing 0, 2.5, 5, 10, 15, and 20% of solid polymer latex (by weight), were prepared and tested in the fresh and hardened states. The test parameters include the fluidity, compressive and flexural strengths, porosity accessible to water, adhesion to clay bricks, and cementitious substrates. The experimental results showed that substituting cement into modified mortars improves their fluidity and adhesion. In the case of clay substrates, a cohesive failure occurs within the substrate layer beyond 10% of substitution, while the rupture takes place at the interface for all formulations tested on cementitious substrates. It was also noted that the flexural tensile strength improved beyond 60 days. However, the compressive strength of polymer mortars decreased with the substitution rate of cement, for all maturities considered. However, for porosity accessible to water, the results follow a linear function, with an inflection at 5% of latex substitution.     

Opal-A rich additives used in ancient lime mortars

Ancient stone and brick masonry mortars from three monuments in Konya, Central Anatolia dated to the Anatolian Selçuk Period (12th and 13th centuries AD) were examined for their raw material composition and durability characteristics to understand some characteristics of medieval mortar technology.Optical microscopy, XRD, SEM, EDX, FTIR and TGA analyses revealed that the mortars contained high percentage of lime binder totally carbonated into micritic calcite. Coarse and medium aggregates were mainly composed of sandstone and metamorphic rock fragments, quartz, feldspar and mica minerals. Opal-A was found in considerable amounts in the fine aggregates, likely not derived from the coarser ones but added separately. Pozzolanic activity of the fine aggregates was determined by conductometric measurements. Their ability to form C-S-H was observed by treating them with saturated Ca(OH)₂ solution.Bulk density and total porosity measurements showed that the mortars were highly porous due to the use of high amount of lime. On the other hand, they possessed sufficient mechanical strength. Mechanical properties were determined by point load tests and ultrasonic pulse velocity measurements. They were expressed as uniaxial compressive strength (UCS) and modulus of elasticity (E_mod) in MPa.The results were also discussed in terms of durability characteristics of the mortars. They were expressed with the use of uniaxial compressive strengths in dry and wet states, and total porosity values. The mortars were considered to have high durability to wetting and drying cycles but had poor durability to the crystallization of water-soluble salts.     

Hydraulic lime mortars with siloxane for waterproofing historic masonry

Mortars with different content of hydraulic lime and aggregates of a siliceous and carbonaceous nature differing in grain size, were designed for waterproofing historic masonry. The repair mortars design was taken into consideration the physico-chemical properties of the original ones. The water repellency of the designed mortars was enhanced through impregnation with an oligomeric organo-siloxane provided optimum water vapour permeability; this is due to the siloxane coating the capillaries without blocking the pores, as indicated from the slightly modified pore size distribution. The grain size of aggregates and the binder content influence the performance of mortars. Mortars with coarse aggregates develop high mechanical strength; nevertheless, micropores interconnected with macropores are responsible for the low salt-decay resistance. Increase of the binding content enhances the mechanical resistance but decreases the resistance to sulphate solutions, as a consequence of the small capillaries not allowing for salt crystallization. The mortar with the best performance consists of medium aggregates and a binder to aggregate ratio equal to 0.33; pores around 0.2 μm of radius enable salts to crystallize without provoking damage from crystallization pressure. The selected mortar, after fourteen months of application to the masonry, shows neither microcracks nor efflorescence formation.     

The wear of magnesia refractories in electric furnaces for melting cast iron

Conclusions The wear of magnesia refractories, i. e., magnesite, perictase — spinel, and magnesite — chromite bricks and magnesite — phosphate mortar, in the walls of electric furnaces for melting cast iron is the result of the solution predominantly of the periclase crystals and to a lesser extent of the spinel in the lowbasicity ferrosilicate slag melt. Brick of the PShS type proved to be the most durable refractory. The use of high-alumina brick in the roof of the furnaces accelerates the wear of the magnesia bricks in the walls.To increase the durability of the lining of these furnaces trials should be carried out with an all-basic wall lining constructed of high-density PShSP-type brick on MF-1-type magnesite — phosphate mortar and a roof lining constructed of MKhS brick and the same mortar.Translated from Ogneupory, No. 4, pp. 44–49, April, 1976.     

硅灰改性水泥/石灰砂浆微观结构的研究

以水泥和石灰为胶凝材料,中细砂为集料,再掺加有机聚合物流化剂制成水泥/石灰砂浆,水泥/石灰砂浆中添加外加剂的文献资料很少,通常是有关水泥砂浆的研究.本实验用硅灰取代10%(质量分数)的普通硅酸盐水泥,水泥、石灰和砂子的质量比为3:1:12,外加有机聚合物对砂浆改性,利用扫描电子显微镜、能谱仪和压汞仪对浆体进行微观分析.分析结果显示,由于硅灰的加入,浆体内部水化产物在早期先以Ⅲ型C-S-H凝胶的形式出现,随后,Ⅲ型和I型的C-S-H凝胶以并存的形式在水化后期出现;正如预期的那样,试样的总的孔隙率也比没加硅灰前有了大幅度的下降,而抗压强度的提高在水化后期才表现出来.     

硫酸盐浸泡环境下CaO-Na2CO3激发矿渣砂浆性能退化及机理研究

以Na₂SO₄和MgSO₄溶液为侵蚀介质,研究了在浸泡环境下CaO-Na₂CO₃激发矿渣(CNS)砂浆和普通硅酸盐水泥(OPC)砂浆经硫酸盐侵蚀前后的抗折强度、抗压强度及不同深度处的SO^2-₄浓度,结合X射线衍射(XRD)、扫描电子显微镜(SEM)、压汞法(MIP)等测试方法分析了CNS砂浆和OPC砂浆的侵蚀产物及孔结构,对比讨论了Na₂SO₄和MgSO₄对CNS砂浆和OPC砂浆的侵蚀机理。结果表明:CNS砂浆的水化产物主要是低Ca/Si比的水化硅铝酸钙(C-A-S-H),不存在氢氧化钙,碳酸钙的填充作用使其孔结构优于OPC砂浆,并且在相同侵蚀环境下,CNS砂浆的抗硫酸盐侵蚀能力大于OPC砂浆;MgSO₄侵蚀环境下CNS砂浆的侵蚀产物主要是水镁石(腐蚀后期会带动试件表面的砂浆一起剥落)和无黏聚力的水化硅铝酸镁(M-A-S-H);与Na₂SO₄相比,MgSO₄对CNS砂浆的腐蚀性更强。