Factors affecting the water retaining characteristics of lime and cement mortars in the freshly-mixed state

Desorptivity, the parameter which quantifies water retaining ability, has been determined for freshly-mixed natural hydraulic lime and cement mortars using a modified American Petroleum Institute pressure cell. The results show how greatly this ability depends on hydraulicity. Mix composition is also highly significant: smaller proportion of sand, larger grain size of sand and higher proportion of mix water all decrease the water retaining ability. In practice water is abstracted due to the capillary pressure of the masonry unit and the results presented are discussed in terms of typical capillary pressures exerted by clay facing brick. Changes in desorptivity also occur with elapsed time from mixing. The most hydraulic mortars become less water retaining for about 90 min after mixing and then, gradually more water retaining.     

Influence of cement kiln dust on the physical properties of calcium lime mortars

This work investigates the influence of cement kiln dust (CKD) on the properties of mortars made with a non-hydraulic binder of high available-lime content (calcium lime—CL), in order to further recycle industrial waste. Physical properties of CKD-CL90 mortars with increasing CKD content were compared to those of feebly-hydraulic lime (NHL2) and CL90 mortars. This paper concludes that, despite the CKD in this study being partially inert, the abundant reactive, free lime provided by the CL90 binder has enabled formation of hydration products. The strength development, rising proportionally to the amount of CKD when addition is over 5%, and the reduction in porosity/suction of the CKD/CL90 mixes, support the occurrence of hydraulic set. The high alkalinity of the CKD/CL90 system; the high specific surface of the CKD particles and the presence of amorphous reactive silica further support the presence of hydraulic set. Results evidenced that CKD addition significantly increased the mortar’s water demand simultaneously enhancing compressive strength and bulk density, and decreasing porosity and capillary suction. These effects can be ascribed to both the gain of packing density induced by the CKD particles, and the formation of hydration phases within pores and the space originally filled with water. Finally, this work concludes that the physical properties of CKD/CL mortars including at least 20%CKD are comparable to those of feebly hydraulic lime mixes, however, fracturing by shrinkage (due to high water demand) and damage related to sulphur, chlorine and alkali content need to be investigated before CKD/CL mixes are advised for application.     

The influence of supplementary cementing materials on water retaining characteristics of hydrated lime and cement mortars in masonry construction

The purpose of this paper is an investigation of the possible role of supplementary cementing materials (SCMs) on the water retaining ability of hydrated lime (CL90) and Portland cement (PC) mortars. Desorptivity (R) defines the water retaining ability of mortars in the freshly-mixed wet state. Transfer sorptivity (A) defines the ability of the substrate to withdraw water from the wet mix. The time to dewater (t _dw), is an expression derived from the sharp front theory, and enables calculation of the time taken for a wet mortar joint to be dewatered by an absorbent substrate. The results show that the very water retaining CL90 mortars become progressively more water releasing with increased volume fraction replacement levels of both ground granulated blast-furnace slag (GGBS) and fly ash (FA). On the other hand, the very water releasing PC mortars become more water retaining with the addition of silica fume (SF). Results also show that transfer sorptivity increases as the volume fraction replacement levels of GGBS and FA increases in CL90 mortars and decreases with increased volume fraction replacement levels of SF in PC mortars. Since the time taken to dewater a mortar joint (t _dw) is inversely proportional to the squared transfer sorptivity, t _dw can be dramatically altered by the addition of SCMs in both CL90 and PC mortars. These parameters have important practical consequences, not only in the initial adhesion of the mortar to the substrate but also in the strength of the set material. The ability to manipulate the water retaining properties can also allow construction time to be reduced.     

Fine ceramics replacing cement in mortars Partial replacement of cement with fine ceramics in rendering mortars

The main objective of the use of very fine red clay ceramic waste in rendering mortars is the reduction in the primary binder (cement) content made possible by the potential pozzolanic effect of this recycled material, with very clear environmental benefits in the reduction of overly-high energy consuming cement and economic benefits in the potential reduction of the cost of mortars. This paper presents an experimental program where ceramic waste crushed to very fine particles was used to partially replace cement in mortars manufacturing, acting as a secondary binder. A large number of tests of the most relevant characteristics of various mortars in which this principle was applied were performed and compared with the results of the same tests in a reference rendering mortar with no ceramic fines (and no reduction of the cement content). The results are most promising both from a performance-based and an environmental point of view.     

A comparative study of the durability and behaviour of fat lime and feebly-hydraulic lime mortars

Lime mortars are often used for repairs to historic buildings. This paper investigates two forms of lime binder: fat and feebly-hydraulic, in order to predict their long-term behaviours and hence ascertain which of the two possesses greater durability, so that they may be used more efficiently in restoration. Mortars were tested for properties governing moisture movement and also subject to durability cycles. The resistance to damage under freezing conditions was evaluated with the saturation coefficient. Thermal cycles had no effect on the mortars and gave no indication of the relative durabilities of the binders. Salt crystallization cycles, though effective in distinguishing the more durable of the two, were too aggressive to gauge a clear profile of salt weathering and succeeded in rapidly decomposing the samples. Tests on the properties governing moisture movement produced good indications of the degree to which the mortars permit flow through their fabrics. According to the results obtained, fat lime mortars are more durable than those made with feebly-hydraulic lime. The results also suggest that the feebly-hydraulic lime mortars are at a higher risk of decomposition by granular disintegration whereas fat lime mortars are better suited to damp, slightly exposed conditions. These results disagree with the general opinion that hydraulic limes are more durable than fat limes due to the additional strength and water insolubility arising from their hydraulicity.     

Strength development and lime reaction in mortars for repairing historic masonries

In this research, restoration mortars with analogous chemical composition of binders, aggregates and mineral additions, as they derive from the study of historic mortars, were evaluated regarding the strength development and the lime reaction, up to 15 months of curing. For this purpose several mixtures were tested in laboratory regarding their chemical and mechanical characteristics. The obtained results show that most of them present a slow rate of chemical and mechanical evolution, with the exception of hydraulic lime mortar and mortar with lime putty–natural pozzolanic addition. The best mechanical behavior was observed in mortars with lime powder and lime powder–artificial pozzolanic addition. These materials present also a low ratio of compressive to flexural strength (f_c/f_f). Further investigations on these materials would determine the time where their chemical and mechanical characteristics become stable. Only at that time, it would be possible to compare the compatibility characteristics of the restoration mortars with those employed in the past.     

How clayey fines in aggregates influence the properties of lime mortars

Despite the fact that the maximum content of fines in aggregates is restricted in national and international standards, the use of unwashed sands in restoration mortars is often demanded by restorers due to their colouring properties. The colour of these aggregates may be caused by clay minerals in the fine fraction below 63 μm. Hence, this study aims to determine the influence of loam and clay contents in a quartz aggregate on the properties of fresh and hardened lime- and lime-cement-mortars. The experimental results revealed that the main effect of clay fines in aggregates is an increase of the water demand for a constant mortar consistency. As a consequence, the higher water/binder ratio causes a strong decrease of the mortar quality with respect to mechanical, hygral and durability properties.     

Compressive strength development of binary and ternary lime–pozzolan mortars

This study considers the compressive strength development of broad range of hydraulic lime mortars prepared with a range of commercially available alumino-silicate by-products and modern pozzolanic additions. Specifically this paper considers the effect of mineral addition selection, binary and ternary combinations, pozzolan content and the effect of curing conditions on the compressive strength development of hydraulic lime based mortars. The study was undertaken as the initial phase of a broader investigation considering the feasibility of producing modern, sustainable hydraulic lime–pozzolan concretes with comparable strengths to Portland cement based concretes. The aim of the initial phase was to identify a small number of additions, and combinations thereof, which would result in a structural strength lime–concrete when scaled up from mortars to concretes.In the absence of a definitive source of information on the mechanical properties of hydraulic-lime mortars prepared with binary and ternary combinations of alumino-silicate by-products, 22 combinations consisting of Natural Hydraulic Lime (NHL5) and a range of possible additions, identified from historical and current practice, were prepared. The results have shown that combining an eminently-hydraulic NHL5 with silica fume and ground granulated blastfurnace slag can produce mortars with a 28-day compressive cube strength of around 28 N/mm², at a water-to-binder (w/b) ratio of 0.5. This is eight times the strength of an equivalent mortar prepared with NHL5 alone and broadly speaking comparable with that of low-heat cementitious mortars. The contribution of the pozzolanic reaction to the strength of hydraulic lime mortars is discussed for a range of alumina-silicious materials and combinations thereof.     

Cohesion aspects in rheological behaviour of fresh cement mortars

The cohesion of fresh cement mortars was measured with a device currently used for shear test on clays, the Laboratory Vane. The effect of the water/cement ratio and the specific surface of the cement on cohesion was examined. The influence of the addition of a superfluidizer based on melaminic resins on the cohesion, flow and compressive strength of the mortars was investigated.

---

Résumé Dans cet article on considère une composante du seuil de cisaillement des mortiers de ciment à l'état frais, la cohésion, mesurée avec un appareil normalement employé pour essayer le comportement au cisaillement des argiles, le ≪Laboratory Vane≫ On examine l'influence de la teneur en eau du mortier et de la surface specifique du ciment sur la cohésion, en déterminant l'existence d'un intervalle de rapports eau/ciment critiques (0,46–0,48), indépendant de la surface spécifique du ciment, où la cohésion du mortier est maximale et sa valeur est une fonction de la surface spécifique du ciment. Le rapport eau/ciment critique représente la limite inférieure du champ du comportement plastique du mortier et peut être défini comme la limite de plasticité. L'addition aux mortiers de ciment d'un adjuvant superplastifiant à base de résines de mélamine provoque le glissement de la limite de plasticité vers des rapports eau/ciment plus bas, au-dessous de 0,40 pour une addition de 5% en poids de ciment. On examine l'influence de l'addition d'adjuvant en différents pourcentages sur l'écoulement, la cohésion et la résistance mécanique dans un mortier plastique.

---

     

Steel protection capacity of polymeric based cement mortars against chloride and carbonation attacks studied using electrochemical polarization resistance

This work analyzes the protection capacity of modified Portland cement mortar with polymers: styrene butadiene, acrylic latex with reinforced plastic fibres and acrylic latex with silica fume, using the electrochemical polarization resistance (R_p) technique to monitor the behaviour of steel bars embedded in the specimens, when placed in environments with CO₂ and chloride. Results indicate that only chemical, physical and mechanical characterizations are not sufficient to classify these materials from the point of view of protection against aggressive agents. There is evidence that material performance depends on workability, chemical composition of squeezed pore solution in addition to the porosity and resistivity which have an important role in the protection against the corrosion of steel bars.     

The role of aggregates on the structure and properties of lime mortars

Lime mortars have been used for centuries in civil engineering construction. Considering ancient monuments and historical buildings it seems that these mortars have proved to be durable and reliable materials although they are of low strength in comparison with cement mortars. Nowadays, they are used for the repair of monuments and for the manufacture of renderings and plasters.

In the present paper the role of aggregates on the structure and behaviour of lime mortars is examined by studying the influence of the aggregate content and the grain size on strength, porosity and volume stability of the mortars. Capillary porosity by suction was also measured as an indicator of resistance to weathering. It is shown that coarse aggregates contribute to the volume stability of lime mortars independent of strength enhancement when adequate compaction reduces the capillary pores. The highest strength values, and consequently, the low porosity, were attained by lime mortars of low binder/aggregate ratio which contained aggregates of maximum size 0–4 mm.     

The effect of chemical admixtures and mineral additives on the properties of self-compacting mortars

Mortar serves as the basis for the workability properties of self-compacting concrete (SCC) and these properties could be assessed by self-compacting mortars (SCM). In fact, assessing the properties of SCM is an integral part of SCC design. The objective of this study was to evaluate the effectiveness of various mineral additives and chemical admixtures in producing SCMs. For this purpose, four mineral additives (fly ash, brick powder, limestone powder, and kaolinite), three superplasticizers (SP), and two viscosity modifying admixtures (VMA) were used. Within the scope of the experimental program, 43 mixtures of SCM were prepared keeping the amount of mixing water and total powder content (portland cement and mineral additives) constant. Workability of the fresh mortar was determined using mini V-funnel and mini slump flow tests. The setting time of the mortars, were also determined. The hardened properties that were determined included ultrasonic pulse velocity and strength determined at 28 and 56 days. It was concluded that among the mineral additives used, fly ash and limestone powder significantly increased the workability of SCMs. On the other hand, especially fly ash significantly increased the setting time of the mortars, which can, however, be eliminated through the use of ternary mixtures, such as mixing fly ash with limestone powder. The two polycarboxyl based SPs yield approximately the same workability and the melamine formaldehyde based SP was not as effective as the other two.     

Bentonite as a natural additive for lime and lime–metakaolin mortars used for restoration of adobe buildings

This work estimates the behaviour of mortars based on lime, seeking their application as renders of adobe walls. Mortars with binder:aggregate 1:3 volumetric ratio were prepared as is traditionally used in old buildings in central parts of Portugal.Due to specificity of the support, two clays, natural clay bentonite (5 wt.%) and artificial clay metakaolin (20 wt.%) were used as additives to lime mortar to prepare 3 types of blended mortars, besides the air lime reference mortar. Mortar prisms 4 × 4 × 16 cm were analysed to assess mechanical properties and salt resistance. Moreover, the mortars were placed in three ways on old adobes taken from demolished houses and their behaviour was verified by artificial accelerated ageing test. Lastly, mortars were applied on a wall made from traditional adobes, where panels were monitored and trials with adhesion strength and Karsten tubes have been conducted. The results obtained by comparison of the characteristics from all the experimental procedures reveal that mortar containing air lime and 5 wt.% of bentonite fulfils in the best way the requirements in its use as render of adobe buildings.     

Rheology of semi-solid fresh cement pastes and mortars in orifice extrusion

Short fiber-reinforced semi-solid fresh cement pastes and mortars, tailored for extrusion, have much lower water-to-binder ratio and higher viscosity than normal cement pastes or mortars. The rheology of these pastes or mortars cannot be characterized by traditional rheology test methods suitable for normal fresh cement pastes or mortars with much greater water-to-binder ratio and lower viscosity. In this paper, orifice extrusion is employed to calibrate rheology of the semi-solid fresh cement mortar. An analytical model is developed for orifice extrusion of semi-solid pastes and mortars obeying a rigid-viscoplastic constitutive relationship, von-Mises yield criterion and the associated flow rule. Orifice extrusion results are interpreted using the analytical model and the established experiment data interpretation method, and the associated rheological parameters are derived for the semi-solid fresh cement mortar. This study provides a simple analytical model, together with experiment and data interpretation methods, for characterizing the complex intrinsic rheological behavior of semi-solid fresh cement pastes or mortars.     

Self-healing of surface cracks in mortars with expansive additive and crystalline additive

This research studies the self-healing potential of cement-based materials incorporating calcium sulfoaluminate based expansive additive (CSA) and crystalline additive (CA). Mortar specimens were used throughout the study. At the age of 28 days, specimens were pre-cracked to introduce a surface crack width of between 100 and 400 μm. Thereafter, the specimens were submerged in water to create a self-healing process. The experimental results indicated that the mixtures with CSA and CA showed favorable surface crack closing ability. The optimal mix design was found to be a ternary blend of Portland cement, 10 wt.% CSA and 1.5 wt.% CA, by which a surface crack width up to about 400 μm was completely closed, and the rate of water passing was dropped to zero within 28 days. It was hypothesized that the amount of leached Ca²⁺ from the matrix plays an important role on the precipitation of calcium carbonate which is the major healing product. The analyses showed that those specimens with CSA/CA additions released more Ca²⁺ than that control specimen. Moreover, those specimens with additives had higher pH value which would favor calcium carbonate precipitation.     

Properties of some cement stabilised compressed earth blocks and mortars

Findings from an on-going investigation into the effects of soil properties and cement content on physical characteristics of compressed earth blocks and soil mortars are presented. A series of test blocks were fabricated using a range of composite soils, stabilised with 5% and 10% cement, and compacted with a manual press. Results for saturated compressive strength, drying shrinkage, wetting/drying durability, and water absorption testing are presented in the paper. In conjunction with the block tests, workability and compressive strength characteristics of suitable soil: cement and cement: lime: sand mortars were also studied. Mortar consistency was assessed using cone penetrometer and slump tests. Water retention properties of the mortars were also measured. For a given compactive effort, the strength, drying shrinkage, and durability characteristics of the compressed earth blocks improved with increasing cement and reducing clay content. Slump testing proved the most reliable means of assessing soil: cement mortar consistency. Both the flow table and cone penetrometer tests were found to be unsuitable. Water retention properties of soil: cement mortars appear well-suited to typical unit water absorption characteristics. Mortar strengths were closely related to cement and clay contents, but as expected were less than the average unit strengths.     

Early shrinkage of cement pastes,mortars, and concretes

In the contribution the authors present measurements of volume changes for cement pastes, mortars, and concretes in an early stage of their hardening. The proposed method makes it possible to measure volume changes from the first setting phase of the measured sample. A contact measurement is made with the aid of inductance transducers. The values of volume changes of the mixture are transmitted by the aid of built-in probes. The temperature of the mixture and of the ambient air was measured by resistance thermometers. All measured values were investigated in set up time intervals by the aid of a measuring station. The investigated mixtures were made of type SC 70 cements for concrete pavements. The composition of the various mixtures is given in the paper. Measurements were carried out at a temperature of 20±1°C and a relative humidity of 50±3%. Most investigations lasted 24 to 48 hours. The measurement results are given in the enclosed illustrations.     

On the correlation between porosity and strength in high-alumina cement mortars

The evolution in time of the strength and porosity of mortars made with the same type of high-alumina cement and two different types of aggregate, calcareous and siliceous, is studied, and the effects of aggregate composition on both parameters are analysed. It is found that between strength and porosity a linear correlation exists. The effects of pore diameter on such correlation is investigated and it is ascertained that the best correlation can be obtained for total cumulative porosity. The results show that this correlation can be useful for the determination of compressive strengthin situ.

---

Résumé On étudie l’évolution dans le temps de la résistance et de la porosité de mortiers confectionnés avec le même type de ciment alumineux et deux types différents de granulats, calcaire et siliceux, et on analyse les effets de la composition du granulat sur les deux paramètres. On constate qu’il existe une corrélation linéaire entre la résistance et la porosité. On examine les effets du diamètre des pores sur une telle corrélation et on établit qu’on peut obtenir la meilleure corrélation pour la porosité totale. Les résultats montrent que cette corrélation peut servir pour déterminer la résistance à la compressionin situ.

     

The petrography and microstructure of medieval lime mortars from the west of Scotland: Implications for the formulation of repair and replacement mortars

Twelfth and thirteenth Century lime mortars from the west of Scotland were examined using optical polarising microscopy and SEM on impregnated, polished thin sections, and of fracture surfaces by secondary electron SEM. The non-hydraulic calcite binder in these mortars is loclly inhomogenouse, exhibiting variations in texture and density. Spongiform binder with porosity of size 10–20μm has sharp transitions with neighbouring zones of dense binder. Sub-isopachus concentrically accreted calcite pore linings delineate extensive areas of secondary porosity created by dissolution of binder. Common lime inclusions (lime lumps) suggest that hot mixing processes were used. Textural characteristics of lime lumps are similar to reaction rims on partially burnt primary source limestone suggesting that provenance for the lime can be deduced from the petrographic features of incompletely burnt relics. The evidence for the dissolution and reprecipitation of carbonate binder materials suggests the need for a careful reconsideration of practical historic mortar analysis. These historic mortars are texturally and compositionally more complex than their modern equivalents. These textures provide evidence for historic lime burning and mortar mixing practices in Scotland during the middle ages, as well as ageing processes, and allows the possibility of a more sophisticated approach to formulating compatible replacement mortars.

---

Résumé Les échantillons de mortiers de chaux, utilisés aux douzième et treizième siècles dans l’ouest de l’écosse, ont été examinés par un microscope optique polarisé et un microscope électronique à balayage (MEB) sur des fines sections polies et des surfaces fracturées par des électrons secondaires d’un MEB. La calcite non-hydraulique dans ces mortiers était hétérogène étant donné la variation de sa texture et de sa densité. La porosité spongieuse, ayant des diamètres de 10–20 μm, présente des transitions d’une zone dense du mélange à une autre zone. Dans la porosité secondaire créée par la dissolution du mélange, la calcite a été déposée sur la surface intérieure. Les inclusions dans la chaux suggèrent qu’un mélange à chaud a été utilisé. Les caractéristiques de la texture de ces inclusions sont similaires à celles d’une calcite issue d’une cuisson primaire partielle. Il semblerait donc que la provenance de la chaux peut être déduite à partir de l’analyse pétrographique des restes de mortier ayant subi une cuisson incomplète. La dissolution et la reprécipitation du carbonate dans le mortier conduisent donc à reconsidérer l’analyse pratique des mortiers historiques, car ils ont une texture et une composition beaucoup plus complexes que leurs équivalents modernes. La texture des mortiers historiques de l’écosse prouve que la cuisson et les pratiques de malaxage ainsi que le processus de vieillessement permettent une approche plus sophistiquée pour formuler les mortiers de remplacement compatibles.

---

---

Editorial Note Dr. John J. Hughes is a RILEM Senior Member. He participates in RILEM TC 167-COM: ‘Charaterisation of old mortars with respect to their repair’.