Freeze–thaw resistance of blended cements containing calcined paper sludge

This work deals with the frost resistance of blended cements containing calcined paper sludge (source for metakaolin) as partial Portland cement replacements. Freeze–thaw tests were performed on blended cement mortars containing 0%, 10% and 20% waste paper sludge calcined at 650 °C for 2 h. Cement mortar specimens were exposed to freezing and thawing cycles until the relative dynamic modulus of elasticity fell below 60%. The performance of the cement mortars was assessed from measurements of weight, ultrasonic pulse velocity, compressive strength, mercury intrusion porosimetry and SEM. Failure of the control cement mortar occurred before 40 freeze/thaw cycles, while cement mortar containing 20% calcined paper sludge failed after 100 cycles. After 28 and 62 freezing and thawing cycles, cement blended with 10% and 20% calcined paper sludge exhibited a smaller reduction in compressive strength than the control cement.     

Mortars with nano-SiO2 and micro-SiO2 investigated by experimental design

This paper reports the effects of nanosilica (nS) and silica fume (SF) on rheology, spread on flow table, compressive strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortars up to 28 days. Samples with nS (0–7 wt.%), SF (0–20 wt.%) and water/binder ratio (0.35–0.59), were investigated through factorial design experiments. Nanosilica with 7 wt.% showed a faster formation of structures during the rheological measurements. The structure formation influences more yield stress than plastic viscosity and the yield stress relates well with the spread on table. Compressive strength, water absorption and apparent porosity showed a lack of fit of second order of the model for the range interval studied. In addition, the variation of the unrestrained shrinkage and weight loss of mortars do not follow a linear regression model. The maximum unrestrained shrinkage increased 80% for nS mortars (7 days) and 54% (28 days) when compared to SF mortars in the same periods.     

Properties of cement mortars containing clinoptilolite as a supplementary cementitious material

This paper presents a study of the properties and behavior of cement mortar with clinoptilolite which is one of the most common zeolite minerals found in nature. Six mortar mixtures were prepared by replacing the Portland cement with 0%, 5%, 10%, 15%, 20% and 30% clinoptilolite by weight. Test results showed that water demand, soundness and setting times of the cement pastes increased with the increase of clinoptilolite content. Compressive and flexural strength of the mortars containing clinoptilolite were higher than the control mixture. Dry unit weight of the mortars with clinoptilolite was lower than the control mortar. Clinoptilolite replacement decreased water absorption and porosity of the mortars. The control mortar showed less durability to carbonation compared to the mortars made with clinoptilolite at the end of carbonation tests. Freeze–thaw resistance of the mortars containing 5% clinoptilolite was higher than control mortar. The effect of clinoptilolite incorporation on high-temperature resistance seemed to be dependent on amount of clinoptilolite, temperature level, and the cooling method.     

Valorization of galvanic sludge in sulfoaluminate cement

Every year increasing amounts of industrial waste are generated worldwide. Depending on their characteristics, wastes can represent an important source of secondary raw materials in order to replace natural resources. In this study, galvanic sludge (LDG) was used as raw material in sulfoaluminate cement. This waste was incorporated to sulfoaluminate cement (CSA), at a weight ratio of 25%, to compose an blended sulfoaluminate cement (BCSA). The compressive strength, drying shrinkage and products of hydration were determined. The efficiency of CSA towards the retention of chromium (the main pollutant present in the sludge) was also investigated. Compressive strength higher than 30 MPa was obtained. The main product of hydration (ettringite) was also identified and the encapsulation of Cr in hydration phases was verified.     

Study on early-age cracking of cement-based materials with superplasticizers

The addition of superplasticizers is an important approach to prepare high performance cement-based materials. The effect of polynaphthalene series superplasticizer (PNS) and polycarboxylate type superplasticizer (PC) on early-age cracking and volume stability of cement-based materials was investigated by means of multi-channel ellipse ring shrinkage cracking test, free shrinkage and strength test. The general effect of PNS and PC is to increase initial cracking time of mortars, and decrease cracking sensitivity of mortars. As for decreasing cracking sensitivity of mortars, PC > H-UNF (high-thickness-type PNS) > C-UNF (common-thickness-type PNS). To incorporate superplasticizers is apparently to increases free shrinkage of mortars when keeping the constant W/B ratio and the content of cement pastes. As for the effect of controlling volume stability of mortars, PC > C-UNF > H-UNF. Maximum crack width of mortars with PC is lower, but the development rate of maximum crack width of mortars with H-UNF is faster in comparison with control mortars. Flexural and compressive strength of mortars and concretes at 28 days increased with increasing superplasticizer dosages under drying conditions. C-UNF was approximate to H-UNF, but PC was superior to PNS in the aspect of increasing strength of cement-based materials.     

Effect of Granulated Blast Furnace Slag and fly ash addition on the strength properties of lightweight mortars containing waste PET aggregates

In this work, the effect of Granulated Blast Furnace Slag (GBFS) and fly ash (FA) addition on the strength properties of lightweight mortars containing waste Poly-ethylene Terephthalate (PET) bottle aggregates was investigated. Investigation was carried out on three groups of mortar specimens. One made with only Normal Portland cement (NPC) as binder, second made with NPC and GBFS together and, third made with NPC and FA together. The industrial wastes mentioned above were used as the replacement of cement on mass basis at the replacement ratio of 50%. The size of shredded PET granules used as aggregate for the preparation of mortar mixtures were between 0 and 4 mm. The waste lightweight PET aggregate (WPLA)–binder ratio (WPLA/b) was 0.60; the water–binder (w/b) ratios were determined as 0.45 and 0.50. The dry unit weight, compressive and flexural–tensile strengths, carbonation depths and drying shrinkage values were measured and presented. The results have shown that modifying GBFS had positive effects on the compressive strength and drying shrinkage values (after 90 days) of the WPLA mortars. However, FA substitution decreased compressive and flexural–tensile strengths and increased carbonation depths. Nevertheless a visible reduction occurred on the drying shrinkage values of FA modifying specimens more than cement specimens and GBFS modified specimens. The test results indicated that, GBFS has a potential of using as the replacement of cement on the WPLA mortars by taking into consideration the characteristics. But using FA as a binder at the replacement ratio of 50% did not improve the overall strength properties. Although it was thought that, using FA as binder at the replacement ratio of 50% for the aim of production WPLA concrete which has a specific strength, would provide advantages of economical and ecological aspects.     

Influence of fine tailings on polyester mortar properties

The purpose of this study is to examine the basic properties of polyester mortars using a fine tailings (FT) from an abandoned mine as a filler. FT with sizes of 10–69 μm is obtained through the centrifugal separation of tailing (TA), and tested for such basic properties, as particle shape, fineness of size distribution, liquid resin absorption, and heavy metal leaching. Polyester mortars with FT and ground calcium carbonate (GC) are prepared with various filler-(filler + binder) ratios and replacements of GC with FT, and tested for working life, flexural and compressive strengths, and chemical corrosion resistance. As a result, FT has almost the same properties as GC in terms of particle shape, fineness of size and liquid resin absorption. The working life of polyester mortars is prolonged with an increased filler-(filler + binder) ratio and replacement of GC with FT. From the vantagepoint of the strength development of the polyester mortars with FT, it is recommended that the filler-(filler + binder) ratio and replacement of GC with FT should be controlled at 50% or less. Mass and strength changes are generally lower in mortars containing FT than in those containing GC in all chemical solutions.     

CDW recycled aggregate renderings: Part II – Analysis of the effect of materials finer than 75 μm under accelerated aging performance

Quality control of the performance of renderings made up of construction and demolition waste (CDW) recycled aggregates needs to be improved as CDW recycling can prove to be an alternative to waste disposal in developing countries. This experimental work focuses the effectiveness of a mix design method to control and analyze the recycled aggregate composition influence on the performance of mortars and renderings. Leveling time in the placement of renderings was also studied. The mix design method of mortars takes into account two parameters: the “aggregates and plasticizing materials to cement ratio” and “the total materials finer than 75 μm” in the dry mortar. In Part I of this study [Construction and Building Materials, submitted to publishing] the basic properties of mortars of several mixes were analyzed for a constant cement content around 155 ± 10 kg/m³. The performance of renderings is the scope of Part II of this paper. The initial bond strength and visible drying cracks under laboratory conditions were first analyzed for renderings applied on masonry panels with two times of leveling during placement. After five months, accelerated aging of renderings was carried out. Ten wetting–drying cycles upon thermal shock, from 80 °C to laboratory room temperature, were applied to the masonry panels, and cracks were assessed for each cycle. Bond tensile strength was not affected by the thermal shock, but additional cracks were seen on the renderings. The mix design parameters of the mortars and their hardened state properties were related to the cracking of the renderings. The results show that the parameters “total materials finer than 75 μm” and “aggregate to cement ratio” can be used for the mix design of mortars with recycled CDW aggregates. The increase in tensile strength and the reduction in the content of total fines smaller than 75 μm have proved efficient parameters to control cracking of renderings under thermal shock. Leveling time during rendering placement was a secondary parameter for cracking behavior.     

Effects of curing regimes and cement fineness on the compressive strength of ordinary Portland cement mortars

Curing techniques and curing duration have crucial effects on the strength and other mechanical properties of mortars. Proper curing can protect against moisture loss from fresh mixes. The objective of this experimental work is to examine the compressive strength of ordinary Portland cement mortars (OMs) under various curing regimes and cement fineness. Six different curing methods including water, air, water heated, oven heated, air–water, and water–air were applied to the specimens and also six groups of mortars were used. The results showed that the highest and lowest compressive strengths are attributed to the specimens of OPC mortar water cured using grounded OPC for duration of 6 h (OM–G6–wc) and OPC mortar air cured under room temperature with oven heated after demoulding of the specimens at 60 °C for duration of 20 h (OM–OH–ac), respectively. The maximum levels obtained of compressive strengths at 7, 28, and 90 days are 57.5, 70.3, and 76.0 MPa, respectively.     

CDW recycled aggregate renderings: Part I – Analysis of the effect of materials finer than 75 μm on mortar properties

Experience shows that renderings produced with natural sands or construction and demolition waste (CDW) recycled aggregates could have a tendency to poor performance, due primarily to the variable quality of the sands, the absence of a well established mix design method for mortars, and other factors such as façade design, substrate quality and the placement technique. This paper focuses some of those factors, particularly the effectiveness of a mix design method for the control and analysis of the influence of the recycled aggregate composition on the properties of mortars and renderings performance. The leveling time of renderings was also studied. The mix ratio of Portland cement, natural fine sand and laboratory recycled sands – from ceramic blocks, concrete bricks and milled mortar – was defined by a mix design method previously studied. The method takes into account two parameters for the mix design of mortars: the “aggregates and plasticizing materials to cement ratio” and “the total materials finer than 75 μm” in the dry mortar. This study analyzes the effectiveness of the second parameter for the control of the performance of mortars and renderings. In Part I, results show how the geology of the river and CDW recycled sands and the “total material finer than 75 μm” parameter can be correlated in order to explain the properties of mortars, as the cement content is kept constant. The variations in water requirement and physical and mechanical properties of mortars were analyzed, namely drying shrinkage, compressive strength, tensile strength and compressive elastic modulus. The performance of the renderings will be discussed in Part II of this paper.     

Lime based steam autoclaved fly ash bricks

About 10 million tonnes of fly ash are produced yearly as waste from coal fired thermal power plants in Turkey. Only a small portion of this waste is utilized as a raw material in the production of cement and concrete. In this study, Seyitömer power plant fly ash was investigated in the production of light weight bricks. Fly ash, sand and hydrated lime mixtures were steam autoclaved under different test conditions to produce brick samples. An optimum raw material composition was found to be a mixture of 68% fly ash, 20% sand and 12% hydrated lime. The optimum brick forming pressure was 20 MPa. The optimum autoclaving time and autoclaving pressure were found 6 h and 1.5 MPa, respectively. The compressive strength, unit volume weight, water absorption and thermal conductivity of the fly ash–sand–lime bricks obtained under optimum test conditions are 10.25 MPa, 1.14 g/cm³, 40.5% and 0.34 W  m⁻¹ K⁻¹ respectively. The results of this study suggested that it was possible to produce good quality light weight bricks from the fly ash of Seyitömer power plant.     

Recycling of municipal incinerator fly-ash slag and semiconductor waste sludge as admixtures in cement mortar

We proposed to tackle the problem of fly-ash pollution from municipal solid waste incineration as well as sludge from chemical–mechanical polishing, by partial substitution of cement in mortar. The optimal modified cement mortar determined by the Taguchi method showed unexpected strengthening effects starting after 4 days of curing and gradually reached a maximum strengthening at 90 days of curing up to 139% of that of ordinary cement mortar. The polluting leachants from the modified cement mortar were barely detectable in toxicity characteristic leaching process tests. The mechanism of the precipitous strengthening effect is preliminarily attributed to nanoparticle activation and enriched hydration.     

Preparation and characterisation of fly ash based geopolymer mortars

Geopolymer mortars with varying levels of sand aggregate were prepared and their physical and mechanical properties studied. The geopolymer binder to sand aggregate weight ratio was varied from 9 to 1. Compressive strength and Young’s modulus of the fly ash based geopolymer paste were 60 MPa and 2.27 GPa and these values did not change significantly with addition of up to 50 wt.% sand aggregate. Geopolymer binder exhibited strong bonding to the sand aggregate. Increasing sand content without increasing the amount of alkaline activator resulted in a decreasing level of geopolymerisation within the binder system.     

Durability of masonry systems: A laboratory study

We deal with the textural aspects, porometry and hydric behaviour of combinations of building materials and their durability under attack by salt crystallisation and freezing. We selected 4 types of lime mortar (pure lime mortar, lime mortar + air-entraining agent, lime mortar + pozzolana and lime mortar + air-entraining agent + pozzolana) which were used in combination with either brick or calcarenite stone. Lime mortars were chosen because they are compatible with traditional building materials, including the bricks and calcarenites that were widely used in the historical buildings that make up our architectural heritage. There are more similarities between the pore size ranges in calcarenites and mortars than there are between those in bricks and mortars. In all cases, a fine layer of calcite microcrystals develops at the contact surface between the mortar and the stone or brick. This is produced by the transformation of the portlandite, which concentrates in this area due to capillary moisture migration. This surface may on the one hand represent an obstacle to the flow of water between the different parts of the system formed by these materials, but on the other it may also favour greater adherence between the components, especially in the calcarenite + mortar combination, which proved to be the most resistant to deterioration in the freeze–thaw tests.     

Influence of activator on the strength and drying shrinkage of alkali-activated slag mortar

The development of new binders, as an alternative to traditional cement, by the alkaline activation of industrial by-products (i.e. ground granulated slag and fly ash) is an ongoing research topic in the scientific community [Puertas F, Amat T, Jimenez AF, Vazquez T. Mechanical and durable behaviour of alkaline cement mortars reinforced with polypropylene fibres. Cem Concr Res 2003;33(12): 2031–6]. The aim of this study was to investigate the feasibility of using and alkaline activated ground Turkish slag to produce a mortar without Portland cement (PC).Following the characterization of the slag, mortar specimens made with alkali-activated slag were prepared. Three different activators were used: liquid sodium silicate (LSS), sodium hydroxide (SH) and sodium carbonate (SC) at different sodium concentrations. Compressive and flexural tensile strength of alkali-activated slag mortar was measured at 7-days, 28-days and 3-months. Drying shrinkage of the mortar was measured up to 6-months. Setting times of the alkali-activated slag paste and PC paste were also measured.Setting times of LSS and SH activated slag pastes were found to be much slower than the setting time of PC paste. However, slag paste activated with SC showed similar setting properties to PC paste.LSS, SH and SC activated slag mortar developed 81, 29, and 36 MPa maximum compressive strengths, and 6.8, 3.8, and 5.3 MPa maximum flexural tensile strengths at 28-days. PC mortar developed 33 MPa compressive strength and 5.2 MPa flexural tensile strength. LSS and SH activated slag mortars were found to be more brittle than SC activated slag and PC mortars.Slag mortar made with LSS had a high drying shrinkage, up to six times that of PC mortar. Similarly, slag mortar made with SH had a shrinkage up to three times that of PC mortar. However, SC activated slag mortar had a lower or comparable shrinkage to PC mortar. Therefore, the use of SC as an activator for slag mortar is recommended, since it results in adequate strength, similar setting times to PC mortar and comparable or lower shrinkage.     

Effects of limestone replacement ratio on the sulfate resistance of Portland limestone cement mortars exposed to extraordinary high sulfate concentrations

A comparative study has been performed on the sulfate resistance of Portland limestone cement (PLC) mortars exposed to extraordinary high sulfate concentrations (200 g/l). PLCs have been prepared by using two types of clinkers having different C₃S/C₂S ratios and interstitial phase morphologies. Blended cements have been prepared by replacing 5%, 10%, 20% and 40% of clinker with limestone. Cubic (50 × 50 × 50 mm) and prismatic (25 × 25 × 285 mm) cement mortars were prepared. After two months initial water curing, these samples were exposed to three different sulfate solutions (Na₂SO₄ at 20 °C and 5 °C, MgSO₄ at 5 °C). Solutions were not refreshed and pH values of solutions were monitored during the testing stage. The compressive strength and length changes of samples have been monitored for a period of 1 year. Additional microstructural analyses have been conducted by XRD and SEM/EDS studies. Results indicated that in general, limestone replacement ratio and low temperature negatively affect the sulfate resistance of cement mortars. Additionally, clinkers of high C₃S/C₂S ratios with dendritic interstitial phase structure were found to be more prone to sulfate attack in the presence of high amounts of limestone.From the results, it is postulated that in the absence of solution change, extraordinary high sulfate content modified the mechanism of sulfate reactions and formation of related products. At high limestone replacement ratios, XRD and SEM/EDS studies revealed that while ettringite is the main deterioration product for the samples exposed to Na₂SO₄, gypsum and thaumasite formation were dominant products of deterioration in the case of MgSO₄ attack. It can be concluded that, the difference between reaction mechanisms of Na₂SO₄ and MgSO₄ attack to limestone cement mortars strongly depends on the pH change of sulfate solutions.     

Investigation of the physico-chemical and microscopic properties of Ottoman mortars from Erzurum (Turkey)

Ottoman mortar is the long-established binding material used for centuries and there are many historical buildings as evidence of its use by Ottomans in Erzurum (Eastern Turkey). The physico-chemical and microscopic properties of the Ottoman mortars in Erzurum have been studied in detail as part of an investigation of the mineral raw materials present in the territory of Turkey. For this purpose, SEM, XRD and EDS analyses of six main types of mortars were carried out showing the presence of organic fibers and calcite, quartz and muscovite minerals. The chemical analyses of the specimens showed that higher SiO₂ + Al₂O₃ + Fe₂O₃ contents yielded in higher values of hydraulicity and cementation indices. A significant result of this investigation was that mortars with higher hydraulicity and cementation indices had higher compressive strengths. Most probably this is the main reason why historical Ottoman buildings were resistant against serious earthquakes.     

Evaluation of sulfate resistance of Portland and high alumina cement mortars using hardness test

Portland cement and high alumina cement mortar specimens were exposed to cycles of drying at 40 °C, cooling at 20 °C and immersion in Na₂SO₄ and MgSO₄ solutions at 20 °C. The resistance of mortars was evaluated by visual inspection and by measuring the change in surface hardness and weight of the specimens. The decrease and increase in surface hardness were observed in both mortars by treating with Na₂SO₄ and MgSO₄ solutions, respectively. The combined effect of the chemical and physical attack by Na₂SO₄ was attributed to the complete failure of Portland cement mortar, whereas only marginal damage of high alumina cement mortar was believed owing to physical salt crystallization. No damage was observed in both mortars treated with MgSO₄ solution.     

Effect of red mud addition on the rheological behaviour and on hardened state characteristics of cement mortars

This paper reports on the use of red mud (RM) in mortars, applying design of experiments. Portland cement was replaced up to 50 wt.% RM, adjusting the relative amount of water (34–38 wt.%) in order to get mortars with suitable workability as defined by rheometry and flow table measurements. Temperature of hydration, compressive strength and water absorption were also determined. RM decreases the workability and increases the torque, but causes lower impact than water variation. The effect on initial yield stress depends on water content. Mortars with similar spread on table show different behaviour along the rheology test. Values of spread on table follow a quadratic model and RM exhibited an interactive effect with water. RM did not change the hydration process, but above 20% the maximum temperature decreases. The reduction of compressive strength is not constant and depends on the water added. Its variation also follows a quadratic model.     

Composition,strength and workability of alkali-activated metakaolin based mortars

This study has investigated the joint effect of several factors on the workability and mechanical strength of alkali-activated metakaolin based mortars. The factors analysed through a laboratory experiment of 432 specimens, pertaining to 48 different mortar mixes were, sodium hydroxide concentration (10 M, 12 M, 14 M, 16 M), the superplasticizer content (1%, 2%, 3%) and the percentage substitution of metakaolin by calcium hydroxide in the mixture (5%, 10%). The results show that the workability decreases with the concentration of sodium hydroxide and increases with the amount of calcium hydroxide and superplasticizer. The results also show that the use of 3% of superplasticizer, combined with a calcium hydroxide content of 10%, allows improving the mortar flow from less than 50% to over 90%, while maintaining a high compressive and flexural strength.