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.     

Physico-chemical study of Cretan ancient mortars

Mortars from monuments of various periods in Crete, from Minoan up to now, have been studied (concerning mineralogical and chemical composition, grain size distribution, raw materials, tensile strength) in order to assess their durability in a marine and humid environment. The lime technology and raw materials, irrespective of the various historic periods, diversify the final composites into mortars, such as: (a) lime, (b) hydraulic lime, (c) lime with crushed brick, and (d) lime with pozzolanic material. These present binders in quantities ranging from 22% (pozzolanic mortars) to 29% (lime mortars). Hydraulic compounds, such as calcium silicate/aluminate hydrates, and tensile strength are higher in the pozzolanic mortars followed by crushed brick lime, hydraulic lime, and lime mortars. High quantities of water-soluble salts identified in the lime mortars indicate their risk of disintegration. A calculation procedure is presented herein, based on the combination of mineralogical and chemical analyses that allows the determination of the binder/aggregate proportion.     

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.     

Mechanical properties of masonry repair dolomitic lime-based mortars

180 different mortars made with a dolomitic lime and different aggregates were prepared in order to be used in restoration works. This paper focuses on the effect of technological variables on pore structure and mechanical properties of magnesian lime-based mortars. Compressive and flexural strengths of the specimens were discussed according to curing time, binder : aggregate ratios, attributes of the aggregates and porosity, at long-term tests.A strong increase in the strength of mortars has been found after 365 curing days as compared to 28 curing days. The strength has been mainly attributed to the portlandite carbonation, because no significant changes have been observed in the brucite. However, higher strengths than similar aerial lime-based mortars led us to think of other mechanism which increases the strength: the calcite formation through a reaction of dedolomitization (alkali carbonate reaction, ACR) and the brucite crystallization were discussed.The pore structure has presented a significant influence on the strength. More binder amounts mean more strength due to the higher values of open porosity, which allows the carbonation process. The aggregate characteristics have been correlated with the strength and porosity. Limestone and angle-shaped aggregates, reducing large pores, cause a strength increment.     

Assessment of phase formation in lime-based mortars with added metakaolin, Portland cement and sepiolite, for grouting of historic masonry

Lime-based mortars containing pozzolanic additions of metakaolin, sepiolite and white Portland cement are studied in order to determine their performance as historic masonry conservation mortars. Hydration products on metakaolin-lime blended mortars include stable and metastable phases. The presence of such products has been studied by means of DTA and XRD analysis, concluding that the selection between them is mainly related with the water-lime ratio. Sepiolite addition to metakaolin-lime mortars has shown to inhibit C₄AH₁₃ formation. Therefore, the influence of phase distribution on the mechanical resistance is considered. Finally, compounds production on blended lime-white Portland cement was compared to natural hydraulic lime ones, and as a result, no remarkable differences appeared, apart from traces of possible cement Portland addition to the latter, usually not mentioned in the nominal composition supplied by the manufacturers of lime binders.     

Study on the replacement of the hydrated lime by kaolinitic clay in mortars

ABSTRACT

Mortars are cement-based materials used mainly to coat and settle construction blocks. In addition to cement, their composition usually includes hydrated lime, sand, and water. The hydrated lime is important to improve the mortar workability. However, lime has a high commercial cost, and its production causes emission of CO₂, a major responsible for global warming. Therefore, the purpose of this work was to investigate the possibility of total or partial replacement of hydrated lime in mortars by a kaolinitic clay with ideal plasticity parameters. Clay amounts of 0, 25, 50, 75, and 100?wt-% were used as replacement of hydrated lime in mortars. The results showed that with up to 50?wt-% of hydrated lime replacement, it is perfectly feasible to fulfil with technological parameters of standards.     

Effects of carbonation on the pore structure of non-hydraulic lime mortars

The pore structures of carbonated non-hydraulic lime mortars made with a range of different aggregates and concentrations of lime have been determined using mercury intrusion porosimetry (MIP). MIP data have been correlated with scanning electron microscopy images and other porosity data. During carbonation there is an increase in pore volume in the ∼ 0.1 μm pore diameter range across all mortar types which is attributed to the transformation of portlandite to calcite. Also there is a monotonic increase in the volumes of pores with diameters below 0.03 μm. A model is proposed for the changes in pore structure caused by carbonation. This attributes the increase in the volume of sub 0.03 μm pores to the attachment of calcite crystals to the surface of aggregate particles, and in some cases to the surface of portlandite crystals. This phenomenon may explain the continuing presence of portlandite in mortars that, apparently, have fully carbonated.     

Setting process of lime-based conservation mortars with barium hydroxide

This paper presents the effect of barium hydroxide on the setting mechanism of lime-based conservation mortars, when used as an additive material. The study focuses on the monitoring of the setting process and the identification of the mineral phases formed, which are essential for furthering the study of the durability of barium mixtures against chemical degradation. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and thermal analysis (DTA-TG) were used to monitor the setting processes of these mixtures and identify new phases formed. The results suggest that barium hydroxide is evenly distributed within the lime and produces a homogeneous binding material, consisting of calcite (CaCO₃), witherite (BaCO₃) and barium-calcium carbonate [BaCa(CO₃)₂]. Finally, it was found that barium carbonate can be directly bonded to calcitic aggregates and therefore increases its chemical compatibility with the binding material.     

The difference in behaviour between calcitic and dolomitic lime mortars set under dry conditions: The relationship between textural and physical–mechanical properties

Differences in the texture, mineralogy, hygric and mechanical properties of mortars prepared with dry hydrated limes of calcitic and dolomitic composition are investigated in this work. Special attention is given to the influence of the lime microstructure and the mortars curing condition. The effect of using two different aggregates (natural and crushed of calcitic and siliceous composition) is also examined. Results showed that the use of dolomitic lime is not recommendable if mortars are applied in dry areas since, under these conditions, a great shrinkage occurs and no strength improvement is induced. Moreover, dolomitic mortars presented a pore network that negatively affects the water transfer properties. On the contrary, calcitic mortars present higher carbonation degree and better physical–mechanical properties. Finally, the use of a calcareous aggregate is preferred because it produces better cohesion in the mortar.     

Correlation of physicochemical and mechanical properties of historical mortars and classification by multivariate statistics

This work uses multivariate statistics in an attempt to classify historical mortars in more or less distinct groups, depending on their physicochemical characteristics. Four types of mortars are studied: “typical lime,” “cementitious,” “crushed brick” and Portland cement. Fifty samples in total were analysed by thermal analyses (differential thermal analysis [DTA] and thermogravimetric analysis [TGA]), mercury intrusion porosimetry and mechanical strength tests. The results give us useful information on the understanding of the technology of historical mortars and planning syntheses for restoration ones. The inverse hydraulicity ratio (CO₂/structurally bound water, SBW) is correlated to CO₂ content (%) as measured by thermal analysis. The tensile strength increases with the amount of hydrated phases and the mechanical properties of the aggregate and the binder. Medians, ranges and extremely rare values were determined for each property showing compact groups. These groups were discriminated by principal component analysis (PCA) giving a tool for characterisation of historical mortars.     

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.     

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.     

Physical and mechanical properties of concrete repair materials in dry and hot-dry environment

A variety of repair materials is available in the market. It is often difficult to select a suitable repair material for a given condition. Various researchers use different evaluation methods, but the required specifications are not established. The main objective of this work is to study the physical and mechanical properties of ready-mixed repair mortars available in the Algerian local market. The experimental study was carried out on three types of repair mortars: cement-based mortars, with and without fibers. The properties of the repair mortars at hardened state are analyzed for compressive, flexural and bond strengths, capillary water absorption, and shrinkage. The effect of humid curing using Hessian regularly humidified, on the compressive strength in hot and dry environment was also studied. The results of the experimental study showed that the repair mortar containing silica fume and synthetic fibers gave a better strength in all curing environments. The study showed also the negative effect of hot and dry environment on all types of ready-mixed repair mortars, and demonstrated the importance of humid curing during early age.     

Study of ancient mortars from Sagalassos (Turkey) in view of their conservation

Since 1990, regular archeological excavations are done in the Roman city of Sagalassos (southwestern Turkey) by the Catholic University of Leuven (Belgium). The mineralogy and petrography of the lime mortars at Sagalassos have been studied in detail as part of an investigation of the provenance of mineral raw materials present in the territory of Sagalassos. The samples were analysed with optical microscopy on thin sections followed by XRD analyses to design a suitable repair mortar. The lime used as binder was burnt from local Triassic limestones and prepared by dry slaking. Three main types of aggregates have been identified: limestone from local Mesozoic limestones, crushed ceramics from locally produced coarse wares and volcanic tuff from a nearby volcanic region. To preserve the excavated remains in very harsh climatic winter conditions, experimental mixtures of restoration mortar have been tested for strength and frost resistance using similar raw materials as in ancient times. The proposed mortar for further on-site conservation and restoration consists of a mix of lime with crushed volcanic rock from the region of Isparta. This composition is very similar to the original Roman material and shows a high frost resistance in freeze-thaw testing.     

Influence of fly ash and its mean particle size on certain engineering properties of cement composite mortars

An experimental investigation on the effects of incorporating large volumes of fly ash on the early engineering properties and long-term strength of masonry mortars is reported. The effect of fly ash and its mean particle size (PD) on the variation of workability and strength has been studied. It was found that fly ash and its mean particle size play a very significant role on the strength of masonry mortars. It has been observed that the early-term strength, except the mortars incorporating coarse fly ash (CFA), was slightly influenced by the replacement with fly ash. The long-term strength (both the bond strength and the compressive strength) will significantly increase, especially for the bond strength of mortars incorporating coarse fly ash. It was also found that the bond strength significantly increased as the mean particle size of fly ash decreases after 28 days curing. However, the 7-day strength was little influenced by fly ash particle size. The fluidity of composite mortar enhanced due to replace cement and lime with fly ash, and the mean PD of fly ash significantly influenced the workability.     

The effect of various slaked limes on the microstructure of a lime-cement-sand mortar

The present work aims to provide a better understanding of the effect of both the proportions and the characteristics of slaked lime on the microstructure of a lime-cement-sand mortar. Cement (CPA CEM I 52.5) has been replaced by various categories of slaked lime chosen for the diversity of their physico-chemical characteristics.Cement has been replaced by lime in proportions varying between 0 to 10% of the total binder mass. With very few exceptions, mortars were produced by maintaining the quantity of water constant.Experimental results show that it is necessary to have a high lime substitution percentage to influence the microstructure of the mortar, except in the case of a lime containing magnesium hydroxide or calcic lime featuring sizeable specific surface area.The influence of the nature of the substituted lime on the development of the microstructure in the matrix has been examined by SEM observations of the mortar micro porosity.     

Lime-pozzolana mortars in Roman catacombs: composition, structures and restoration

Analyses of microsamples collected from Roman catacombs and samples of lime-pozzolana mortars hardened in the laboratory display higher contents in carbonated binder than other subaerial Roman monuments. The measured environmental data inside the Saint Callistus and Domitilla catacombs show a constant temperature of 15-17 °C, a high CO₂ content (1700 to 3500 ppm) and a relative humidity close to 100%. These conditions and particularly the high CO₂ concentration speed-up the lime calcitization roughly by 500% and reduce the cationic diffusion to form hydrous calcium aluminosilicates. The structure of Roman catacomb mortars shows (i) coarser aggregates and thicker beds on the inside, (ii) thin, smoothed, light and fine-grained external surfaces with low content of aggregates and (iii) paintings and frescoes on the outside. The observed high porosity of the mortars can be attributed to cracking after drying linked with the high binder content. Hardened lime lumps inside the binder denote low water/mortar ratios for slaking. The aggregate tephra pyroclasts rich in aluminosilicate phases with accessorial amounts of Ba, Sr, Rb, Cu and Pb were analysed through X-ray diffraction (XRD), electron microprobe analysis (EMPA) and also by environmental scanning electron microscopy (ESEM) to identify the size and distribution of porosity. Results support procedures using local materials, special mortars and classic techniques for restoration purposes in hypogeal backgrounds.     

A chemometric approach to the characterisation of historical mortars

The compositional knowledge of historical mortars is of great concern in case of provenance and dating investigations and of conservation works since the nature of the raw materials suggests the most compatible conservation products. The classic characterisation usually goes through various analytical determinations, while conservation laboratories call for simple and quick analyses able to enlighten the nature of mortars, usually in terms of the binder fraction. A chemometric approach to the matter is here undertaken. Specimens of mortars were prepared with calcitic and dolomitic binders and analysed by Atomic Spectroscopy. Principal Components Analysis (PCA) was used to investigate the features of specimens and samples. A Partial Least Square (PLS1) regression was done in order to predict the binder/aggregate ratio. The model was applied to historical mortars from the churches of St. Lorenzo (Milan) and St. Abbondio (Como). The accordance between the predictive model and the real samples is discussed.     

Durability of traditional plasters with respect to blast furnace slag-based plaster

Blast furnace slag is a residue of steel production. It is a latent hydraulic binder and is normally used to improve the durability of concrete and mortars. Slag could be also used as rendering mortar for masonry and old buildings. Today, cement and hydraulic lime are the most popular hydraulic binders used to make plasters. They are characterised by a low durability when exposed to the action of chemical and physical agents.The aim of this study was to provide a comparison between the physical-mechanical properties of some renders made with ordinary Portland cement, hydraulic lime, or slag. Furthermore, an investigation was carried out to analyse mortar resistance to several aggressive conditions like acid attack, freezing and thawing cycles, abrasion, sulphate aggression, cycles in ultraviolet screening device, and salt diffusion. The specimens, after chemical attack, have been characterised from the chemical-physical [specific surface according to the BET (Brunauer-Emmet-Teller) method], crystal-chemical (X-ray diffraction, XRD), and morphological (scanning electron microscopy, SEM) points of view.     

The Adhesion Properties of Mortars in Relation with Microstructure

The interaction between masonry units and mortar is a crucial factor for the quality of a wall. The most important factor is the adhesion between bricks and mortar in order to construct a masonry wall with adequate strength, good impermeability, and durability. In this work mortars were produced with various cement/lime/aggregates ratio. The adhesion properties of the mortars with clay bricks were tested with a simplified tensile/tear testing measurement. In order to investigate the adhesion properties in relation with microstructure the mortars were characterized with X-ray diffraction and were further investigated with scanning electron microscopy and stereoscopy. It was found that adhesion is favored by the formation of a Si–Al matrix with a low Ca content in the brick/mortar interface and the formation of fine Ca–Al–Si phases which can penetrate into the brick.