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.     

Influence of cement and aggregate type on thaumasite formation in concrete

In this study the influence of binder type on the formation of thaumasite in mortar prisms made with expanded clay lightweight aggregate (LWA) or quartz sand was examined. For this purpose mortar prisms were made, which after 28 days of curing in deionised water were exposed to a sulphate solution or deionised water. The length and weight change of the prisms was recorded in triplicate as a function of time of exposure to dry–wet cycles at 5 ± 1 °C.The influence of the binder type on the expansion in the sulphate solution can be ordered from strong to weak as follows: (1) CEM I + limestone filler, (2) CEM I, (3) CEM I + fly ash, and (4) CEM III/A. Because the porosity of the LWA was able to accommodate the growing sulphate crystals, the mortar prisms made with LWA were still largely intact after 3 years of exposure. The only exception being the mortar prisms containing limestone filler. The mortar prisms made with quartz sand and exposed to the sulphate solution were all bent, broken or disintegrated after 24 weeks. The prisms exposed to deionised water showed minimal expansion. Key factors controlling the formation of thaumasite are discussed.     

Efficiency of ground granulated blast-furnace slag replacement in ceramic waste aggregate mortar

From our previous findings, the recycling of ceramic waste aggregate (CWA) in mortar has been proved an ecological means plus an excellent outcome against chloride ingress. The CWAs were porcelain insulator wastes supplied from an electric power company, which were crushed and ground to fine aggregate sizes. In this study, to further develop the CWA mortar as an eco-efficient construction material, ground granulated blast-furnace slag (GGBS) was incorporated. The slag (having the Blaine fineness of 6230 cm²/g) was utilized as a supplementary cementitious material (SCM) at three different replacement levels of 15%, 30%, and 45% of cement by weight. The efficiency of the GGBS on enhancing chloride resistance in the CWA mortars was experimentally assessed by using a silver nitrate solution spray method and an electron probe microanalysis (EPMA). The tests were carried out on mortar samples after immersed in a 5.0% NaCl solution for 24 weeks. Another set of the mortar samples was exposed to a laboratory ambient condition for 24 weeks and then followed with a carbonation test. The test results indicated that the resistance to the chloride ingress of the CWA mortar becomes more effective in proportion to the replacement level of the GGBS. In contrast, the carbonation depth of the CWA mortar increases with the increase of the GGBS. The activeness of the GGBS was also evaluated on the basis of the compressive strength development up to 91 days. Due to its high fineness, the GGBS can be used up to 30% while the high relative strength (more than 1.0) is achieved at all ages.     

Influence of a new type of additive on the performance of polymer-lightweight mortar composites

This paper shows how a new powder polymer additive (PPA), containing a waterproofing agent, a rheology control agent and air-entrainers, affects the workability, mechanical properties and setting times of polymer-lightweight mortar composites (PLMC). The waterproofing agent was a mixture of redispersible polyethylene vinyl acetate and redispersible silane based polymer powder. The rheology control agent was a redispersible hydroxypropyl carboxymethyl ether of patato starch based polymer powder. Air-entraining agent was a redispersible and an unmodified sodium laurly sulphate based polymer powder. Pumice fine aggregate at 0–3 mm size fraction was used as lightweight aggregate throughout the research work. In order to examine the effects of powder polymer additive on flowability and the performance when the additive is mixed in a mortar, the mixture proportions were set in four trial batches. The volume proportions of cement and pumice lightweight fine aggregate were fixed at 1:9, 1:8, 1:7 and 1:6, respectively, defining the mixture of mortar for measuring the compressive strength and workability of lightweight mortar. In this research study, PLMC mortars with 28 different mixture proportions (M1–M28) by weight of cement contents of 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 1.2% were adopted for the mortar mixture batches, respectively. Flow value of mortar was measured using a flow table method in accordance with the regulation in ASTM C230, “flow table for use in tests of hydraulic cement”. The target flow was fixed at 130 mm for each mixture proportion, which is regarded as the most suitable fluidity to secure workability at a site. For each mixture, 12 fresh plastic mortar samples were prepared according to the method specified in ASTM C305 and cured in a humidified atmosphere for 24 h, removed from the mould after 24 h, cured in water for 7 days, and then cured in air. The compressive strength test results were evaluated in accordance with ASTM C270.The suitability of using a new powder polymer additive in terms of workability and required compressive strength in PLMC mortar applications is also presented in this paper. It is observed that PLMC mortars have adequate strength and more convenient workability for their use in general masonry construction applications.     

A study on the effects of high temperature on mechanical properties of fiber reinforced cementitious composites

The flexural strength and ductility properties of cementitious composites (mortar) under high temperature may be significantly improved by incorporating different types of fibers. In this study, four different types of fibers are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen for research. These fibers are added into mortars in five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mortars are subjected to the following temperatures: 21 °C (normal conditions), 100 °C (oven dry), 450 °C and 650 °C. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. In addition, thin sections of mortars are investigated to obtain changes in mortar because of high temperature. It is concluded that all fiber types contribute to the flexural strengths of mortars under high temperature. However, this contribution decreases with an increase in temperature. The samples with PVA show the best flexural performance (75–150%) under high temperature. CF which does not melt under high temperature also gives high flexural strength (11–85%). The compressive strengths of the mortars reduce under high temperature or with fiber addition. The highest increase in flexural strength and the lowest decrease in compressive strength is at 0.5–1.5% for CF if all temperature conditions are taken into consideration. The optimum fiber addition ratios of the samples containing PP and GF are 0.5% by volume. And for PVA, it is between 0.5% and 1.5% by volume.     

A study on the effect of nano silica on compressive strength of high volume fly ash mortars and concretes

This paper presents the effect of nano silica (NS) on the compressive strength of mortars and concretes containing different high volume fly ash (HVFA) contents ranging from 40% to 70% (by weight) as partial replacement of cement. The compressive strength of mortars is measured at 7 and 28 days and that for concretes is measured at 3, 7, 28, 56 and 90 days. The effects of NS in microstructure development and pozzolanic reaction of pastes containing above HVFA contents are also studied through backscattered electron (BSE) image and X-ray diffraction (XRD) analysis. Results show that among different NS contents ranging from 1% to 6%, cement mortar containing 2% NS exhibited highest 7 and 28 days compressive strength. This NS content (2%) is then added to the HVFA mortars and concretes and the results show that the addition of 2% NS improved the early age (7 days) compressive strength of mortars containing 40% and 50% fly ash by 5% and 7%, respectively. However, this improvement is not observed at high fly ash contents beyond 50%. On the other hand, all HVFA mortars exhibited improvement in 28 days compressive strength due to addition of 2% NS and the most significant improvement is noticed in mortars containing more than 50% fly ash. In HVFA concretes, the improvement of early age (3 days) compressive strength is also noticed due to addition of 2% NS. The BSE and XRD analysis results also support the above findings.     

Identification of admixture for pelletization and strength enhancement of sintered coal pond ash aggregate through statistically designed experiments

Statistically designed experiments using Response Surface Methodology have been undertaken to identify the parameters influencing manufacturing process and properties of aggregate using coal pond ash (generated from bituminous and lignite coal sources). Based on the preliminary studies, Ca(OH)₂ and borax have been identified as pelletization and strength enhancing admixture respectively. Pelletization efficiency of bituminous and lignite pond ash increased with an increase in binder and Ca(OH)₂ dosage to 20–98% and 50–98% respectively, with proportionate quantity of water. Sintering has been used as a hardening method with temperature range of 900 °C and 1100 °C for a duration range of 45–120 min. Phase composition and sintered microstructure of aggregate has been reported using X-ray diffraction and scanning electron microscopy respectively. The ten percent fines value of aggregate with clay binder was 5.5 tonne as against a value of 4.5 tonne with aggregate with bentonite binder. Among the binders studied, bentonite resulted in high volume utilization of pond ash, i.e. up to 88%.     

Effect of SO3 content and fineness on the rate of delayed ettringite formation in heat cured Portland cement mortars

This paper presents the findings of a long-term study on the expansion rate and microstructure of heat cured cement mortars. For this purpose, cements with different fineness and SO₃ contents were produced by using the same clinker. Different mortar specimens were prepared and subjected to heat curing. Length changes of specimens were measured within a period of 540 days. The microstructures of young (2 day after heat curing) and old (1.5 years after heat curing) specimens were also investigated by SEM and EDS analysis. The expansion rates and microstructures observed were compared with the control specimens.Results showed that, at the initial stages of testing (2–3 months), expansion rates of heat cured mortars prepared with finer cements were less than those prepared with coarser cements. However, in the long term, the rate of expansion of mortars prepared with finer cements exceeded the coarser ones’ expansion values. This result may be attributed to the different hydration characteristics and pore structure of heat cured mortars including cements of different fineness.     

Evaluation of accelerated test methods for determining alkali-silica reactivity of concrete aggregates

For assessing the applicability of a newly proposed Chinese accelerated mortar bar test (CAMBT) to overseas aggregates and determining the appropriate aggregate size fraction for the test, the influence of aggregate particle size on ASR expansion was studied at 0.15–0.80 mm, 1.25–2.50 mm and 2.5–5.0 mm size fractions on nine aggregates from a range of sources. Correlation between expansions in the CAMBT and in the accelerated mortar bar test (AMBT), and correlations between the two accelerated tests and the Concrete Prism Test (CPT) were examined. The results indicate that, for most aggregates tested, 0.15–0.80  mm is not the most sensitive aggregate size to expansion in the CAMBT, especially at early period before 10 days. The 1.25–2.50 mm size fraction of all the nine aggregates, gives the highest early expansion (first 10 days). Correlation between expansions in the CAMBT and expansions in the AMBT is satisfactory. However, the correlations in expansions of both AMBT and CAMBT with the CPT are very poor. A better correlation between expansions in the modified CAMBT and in the CPT is obtained when 2.5–5.0 mm aggregate particles was used, but further tests are necessary to establish the full reliability of the test.     

Physical and chemical assessment of lime–metakaolin mortars: Influence of binder:aggregate ratio

This work evaluates the influence of binder:aggregate ratio on the mineralogical and mechanical properties of air lime–metakaolin mortars.Mineralogical analysis showed that binder:aggregate ratio affects the extent of carbonation and pozzolanic reactions with curing. The pozzolanic reaction occurs mostly at lower curing times (28 days), while, at higher curing ages, carbonation reaction is mostly dominant. The exceptions are mortars with 1:1 (air:lime) volumetric ratio with 30% and 50% MK in which the pozzolanic reaction is still dominant.The reduction in the mechanical resistance of some compositions observed from 28 to 90 days is related to the calcium aluminate hydrate instability in the presence of free lime. This instability is expected to disappear after the total consumption of free lime, either by pozzolanic or carbonation reaction.     

Electrostatic self-assembled carbon nanotube/nano carbon black composite fillers reinforced cement-based materials with multifunctionality

Electrostatic self-assembled carbon nanotube (CNT)/nano carbon black (NCB) composite fillers are added into cement mortar to fabricate smart cement-based materials. The grape bunch structure of CNT/NCB composite fillers is beneficial for dispersing CNT/NCB in cement mortar matrix and achieving cooperative improvement effect. The mechanical, electrically conductive, and piezoresistive behaviors of the cement mortar are investigated. The CNT/NCB composite fillers can effectively enhance the flexural strength and electrical conductivity of cement mortars, and endow stable and sensitive piezoresistivity to cement mortar at a low filler content. However, they weaken the compressive strength of cement mortar to some extent. The percolation threshold zone of cement mortar with CNT/NCB composite fillers ranges in the amount of 0.39–1.52 vol.%. The optimal content of CNT/NCB composite fillers is 2.40 vol.% for piezoresistivity and the stress and strain sensitivities can reach 2.69% MPa⁻¹ and 704, respectively.     

Alkali-aggregate behaviour of alkali-activated slag mortars: Effect of aggregate type

The alkali–silica reaction in waterglass-alkali-activated slag (waterglass-AAS) and ordinary Portland cement (OPC) mortars was evaluated using three types of (siliceous and calcareous) aggregates. The tests were conducted to the ASTM C1260-94 standard test method. The mortars were studied by volume stability, mechanical strength and Hg intrusion porosity. The ASR products were studied with XRD, FTIR and SEM/EDX techniques.According to the results obtained, under the test conditions applied in this study, waterglass-AAS mortars are stronger and more resistant to alkali-aggregate reactions than OPC mortars. When the mortars were made with a reactive siliceous aggregate, expansion was four times greater in the OPC than in the AAS material. When a reactive calcareous (dolomite) aggregate was used, no expansion was detected in any of the mortars after 14 days, although the characterization results showed that the dolomite had reacted and calcareous-alkali products (brucite) had in fact formed in both mortars. These reactive processes were more intense in OPC than in AAS mortars, probably due to the absence of portlandite in the latter. When the calcareous aggregate was non-reactive, no expansions were observed in any of the mortars, although a substantial rise was recorded in the mechanical strength of AAS mortars exposed to the most aggressive conditions (1 M NaOH and 80 °C).     

Influence of fired clay brick waste additions on the durability of mortars

The use of metakaolin is known to help improve properties of Portland cement-based mortars. The presumed similarities between the characteristics of metakaolin and those of a powdered (<45 μm) fired clay brick clean waste (CBW) led to the investigation of the effect on the durability of mortars of partial replacement (10, 25 and 40 wt.%) of Portland cement by CBW. Properties such as 28 and 90 days-compressive strength, water absorption, apparent porosity, absorption by capillarity, chloride retention, carbonation depth and sulphate resistance were evaluated. The CBW-containing cured mortars showed improved strength and density, as the result of combined physical and pozzolanic pore filling effect of added CBW. However, CBW-free mortar exhibited larger spreading and, being more porous, higher sulphate resistance and ability to absorb chlorides. Optimum performance was found for the 40 wt.% CBW mortar whose compressive strength can be up to 130% higher than that of the CBW-free mortar.     

Compressive strength and drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement mortars

This paper studies the physical properties, compressive strength and drying shrinkage of multi-blended cement under different curing methods. Fly ash, ground bottom ash and undensified silica fume were used to replace part of cement up to 50% by weight. Specimens were cured in air at ambient temperature, water at 25, 40 and 60 °C, sealed with plastic sheeting for 28 days. The results show that absorption and volume of permeable pore space (voids) of blended cement mortars at 28 day under all curing methods tend to increase with increasing silica fume replacement. The compressive strength of blended cement with fly ash and bottom ash was lower than that of Portland cement control at all curing condition while blended cement with silica fume shows higher compressive strength. In addition, the compressive strength of specimens cured with water increased with increasing curing temperature. The drying shrinkage of all blended cement mortar cured in air was lower than that of Portland cement control while the drying shrinkage of blended cement mortar containing silica fume, cured with plastic sealed and water at 25 °C was higher than Portland cement control due to pore refinement and high autogenous shrinkage. However, the drying shrinkage of blended cement mortar containing SF cured with water at 60 °C was lower than that of Portland cement control due to lower autogenous shrinkage and the reduced microporosity of C–S–H.     

Recycling petroleum coke in blended cement mortar to produce lightweight material for Impact Noise Reduction

This work introduces a new way to use low-cost petroleum (pet) coke as lightweight aggregate in cement mortars to make sound barriers. The feasibility of adding pet coke in cement matrix was investigated: an in-depth characterization of as-received coke and the new lightweight mortar was made. The acoustic behaviour herein was assessed by constructing a large dimension mortar slab (made of cement and coke as aggregate) used as floor covering and measuring, according to the procedure described in international standards, the impact noise pressure level over the range of frequencies 100–5000 Hz. Impact Noise Reduction (INR) was also obtained and the results were compared to the ones experimentally obtained from a control mortar slab (made of cement and sand). Results showed that coke addition leads to a decrease in mechanical properties of resultant mortars, this is principally due to an increase of the porosity (～60%). A gradual increase of impact noise insulation was observed in lightweight floor covering from middle to higher frequencies tested, reaching, within this range, a remarkable improvement of sound insulation compared to control slab (～14 dB).     

Recycling petroleum coke in blended cement mortar to produce lightweight material for Impact Noise Reduction

This work introduces a new way to use low-cost petroleum (pet) coke as lightweight aggregate in cement mortars to make sound barriers. The feasibility of adding pet coke in cement matrix was investigated: an in-depth characterization of as-received coke and the new lightweight mortar was made. The acoustic behaviour herein was assessed by constructing a large dimension mortar slab (made of cement and coke as aggregate) used as floor covering and measuring, according to the procedure described in international standards, the impact noise pressure level over the range of frequencies 100–5000 Hz. Impact Noise Reduction (INR) was also obtained and the results were compared to the ones experimentally obtained from a control mortar slab (made of cement and sand). Results showed that coke addition leads to a decrease in mechanical properties of resultant mortars, this is principally due to an increase of the porosity (∼60%). A gradual increase of impact noise insulation was observed in lightweight floor covering from middle to higher frequencies tested, reaching, within this range, a remarkable improvement of sound insulation compared to control slab (∼14 dB).     

Doubling the service life of concrete structures. II: Performance of nanoscale viscosity modifiers in mortars

A new approach for increasing the service life of concrete structures is evaluated in a series of mortar specimens. The new approach consists of employing nanoscale viscosity modifiers to increase the viscosity of the concrete pore solution and concurrently and proportionally decrease the diffusion rates of deleterious ions such as chlorides and sulfates. In part I of this series, viscosities of bulk solutions of the admixtures in water and electrical conductivities of admixture solutions also containing potassium chloride were examined to verify the viability of this new technology. In the current paper, these studies are extended to quantifying the performance of one of these admixtures in mortars by measuring the penetration depth of chloride ions in cylindrical specimens exposed to a 1 mol/L chloride ion solution for up to 1 year. While significant reductions in the 1 year penetration depth are produced when the viscosity modifier is utilized via conventional addition to the mixing water, the best performance is achieved when a solution of the viscosity modifier is utilized to pre-wet fine lightweight aggregates that are then added to the mortar mixture. A scaling function appropriate for radial diffusion was used to estimate the relative effective diffusion coefficients. Compared to a reference mortar, the best mixture reduced the effective diffusion coefficient by a factor of 2.7, consistent with the overall objective of doubling concrete service life.     

The influence of binder tow density on the mechanical properties of spatially reinforced composites. Part 1 – Impact resistance

This paper examines the influence of binder tow stitch density on the impact performance of advanced composite structures. Spatially reinforced composite reinforcements with multi-axis, multi-layer structures were woven on a specially developed loom. The binder tow stitch density, which was used to consolidate the structure, was varied in the range of 1–4 binder tow stitches/cm² (10 × 10 mm to 5 × 5 mm binder tow stitch spacing). A drop weight impact test (6.7 J/mm of composite thickness) was used to damage the samples. Both the depth of penetration and the damage area were measured after impact. The analysis of the results has shown that as the binder tow stitch density was increased the extent of damage decreased. The weave architecture, in terms of the relative position of the ±45° tows, was also shown to be a significant factor, the nearer the off-axis tows are to the impact surface the greater was the damage area.     

Statistical analysis for freeze–thaw resistance of cement mortars containing marble dust and glass fiber

This paper investigated the usability of marble dust and glass fiber against the harmful effects of freeze–thaw (FT) cycles on cement mortars as experimentally and statistically. To this end, the cement mortar specimens containing marble dust (0%, 20%, 40% and 50% by volume) and glass fiber (0 kg/m³, 0.25 kg/m³, 0.50 kg/m³, 0.75 kg/m³) were prepared. The compressive and flexural strengths of the specimens were determined after being exposed to FT cycles. In order to reduce the numbers of experiments, an L₁₆ (4² × 2¹) Taguchi orthogonal array was adopted to the study. Amounts of glass fiber, percentages of marble dust and cycles of freeze–thaw, were changed to explore their effects on the compressive and flexural strengths of the mortar specimens. Statistically effects of the factors were also determined by using analysis of variance (ANOVA) method. Finally, experimental findings were compared with statistical results and a good agreement between them was achieved.     

Impact response of lightweight mortars containing expanded perlite

This paper describes the mechanical response of lightweight mortars subjected to impact loading in flexure. Expanded perlite aggregate with a bulk density of 64 kg/m³ was used at between 0 and 8 times by volume of Portland cement to yield a range of mortars with density between 1000 and 2000 kg/m³. Some specimens were reinforced with a polypropylene microfibre at 0.1% volume fraction and the dynamic fracture toughness was evaluated by means of an instrumented drop-weight impact system. Companion tests were carried out in compression under quasi-static loading to standardise the mixes. The compressive strength and elastic modulus scale as the cube of the relative density, defined as the ratio of the density of the mortar to that of Portland cement paste. Whereas the flexural strength and fracture toughness were both linearly proportional to the relative density of the mortar under quasi-static loading, there was an increase in their sensitivity to relative density at higher loading rates. Contrary to what is seen in regular concrete, fibre reinforcement led to an increase in the stress-rate sensitivity of flexural strength in lightweight mortars. For the same impact velocity, the stress-rates experienced by a specimen was strongly influenced by its density. While the stress-rate sensitivity of flexural strength dropped with a decrease in the mix density, that of the fracture toughness was consistently higher for the lighter mixes.