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.     

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.     

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 nano-silica on rheology and fresh properties of cement pastes and mortars

Amorphous nano-silica (nS) particles (0–2.5 wt%) by cement were incorporated in cement pastes and mortars, and their effect on the fresh state behaviour was analysed. Rheological tests showed that after 75 min from the mixing start, the mortar having 2.5 wt% nS shows insufficient flowability to allow its continuous monitoring in a Viskomat PC viscometer. The influence of nS content was better observed on yield stress when compared with plastic viscosity values (the first increased about 66.5% while the latter just increased 3.6%). With nS addition, spread, setting time and the moment to reach the maximum temperature decreased 33%, 60% and 51.3%, respectively, when compared with samples without nS. X-ray diffraction showed presence of calcium hydroxide after 9 h in the sample with 2.5 wt% nS. The air content increased 79% and apparent density decreased 2.4% when nS was added.     

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.     

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.     

Combined effect of mineral admixtures with superplasticizers on the fluidity of the blended cement paste

The new concrete often incorporates several organic and mineral admixtures which interact with the various constituents of the cements and cause some problems of hardness and workability. In the present study, limestone cement (C1) and pozzolanic cement (C2) were used to make cement paste with two types of superplasticizer; SP1 based on polynaphthalene sulphonate (PNS); and SP2 based on resins melamines (PRM). Marsh cone test was adopted to check the combined effects of the following factors on the fluidity namely the type of cement, the type and the dosage of the superplasticizer, the type and the replacement rate of the mineral admixture and the water–cement ratio (W/C). The results of this work show that limestone cement presents a high fluidity with low loss after 1 h relatively to the pozzolanic cement within the saturation proportioning. Superplasticizer SP1 constitutes an incompatibility case when it is mixed with cement containing high C₃A or alkali content such as C2 cement. Also, limestone powder is found to be the best mineral admixture when it replaces a part of cement, where more fluidity is exhibited caused by the dilution effect.     

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.     

Enhancement of unconfined compressive strength of sand test pieces cemented with calcium phosphate compound by addition of various powders

To improve the unconfined compressive strength (UCS) of a novel chemical grout composed of a calcium phosphate compound (CPC-Chem), we performed UCS tests and scanning electron microscopy (SEM) observations on sand test pieces cemented with CPC-Chem and four kinds of powders (tricalcium phosphate, TCP; magnesium phosphate, MgP; calcium carbonate, CC and magnesium carbonate, MgC) as seed crystals. The UCS of the CPC-Chem test pieces cemented with TCP and CC was significantly greater than that of the test pieces with no added powders. The UCS of the test pieces with TCP and CC additives exceeded the targeted value of 100 kPa and increased to a maximum of 261.4 kPa and 209.7 kPa for the test pieces with TCP and CC additives, respectively. Furthermore, the UCS of test pieces with 1 wt% or 5 wt% TCP and 1 wt% CC additives was maintained at a level exceeding 200 kPa for 168 days. SEM observations revealed net-like and three-dimensional structures in segments of test pieces cemented with 1 wt% or 5 wt% TCP and 1 wt% CC in CPC-Chem, which could have been the reason of the long-term stability of UCS (over 200 kPa for 168 days) observed in this study. These results suggest that the addition of TCP and CC significantly enhances the ground improvement afforded by CPC-Chem.     

The effect of polypropylene fibers on the properties of fresh and hardened lightweight self-compacting concrete

This paper evaluates the LECA Lightweight Self-Compacting Concrete (LLSCC) manufactured by Nan-Su, of which the Packing Factor (PF) of its design mixing method has been modified and improved.The study analyzes the impact of polypropylene fibers on LLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition.The evaluation of Fiber Reinforced LLSCC (FR-LLSCC) fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability, segregation resistance ability and filling ability of fresh concrete.For the mechanical properties of LLSCC, the study has been conducted as follows: compressive strength with elapsed age, splitting tensile strength, elastic modulus and flexural strength, all of which were measured after the sample being cured for 28 days.When self-compacting concretes were lightened to 75% of their normal weight, their fresh properties are affected immensely.Applying 0.3% volume fractions of polypropylene fiber to the LLSCC resulted in 40% reduction in the slump flow (from 720 mm to 430 mm). In general, the rate of slump flow over Super Plasticizer (SP) volume percentage reduced with the use of polypropylene fibers in the FR-LLSC.Polypropylene fibers did not influence the compressive strength and elastic modulus of LLSCC, however applying these fibers at their maximum percentage volume determined through this study, increased the tensile strength by 14.4% in the splitting tensile strength test, and 10.7% in the flexural strength.     

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.     

Potable water filtration sludge: Use as set retarder in one-coat plastering mortars

This work describes the study of the potential use of the sludge generated in potable water filtration/cleaning operations (waste material) as set retarder and workability-aid in rendering/plastering mortars. A commercial mortar was used as reference and several formulations were investigated, containing the waste material and sodium phosphate instead of sodium or calcium phosphate enriched bentonites, traditionally used as set retarder and workability-aid in cement based compositions. Sodium tri-polyphosphate was also tested alone for the same purpose. Fresh mortars were prepared with a water-to-cement weight ratio of 1.1 and a sand-to-cement weight ratio of 4:1.The results obtained in set time tests suggest that the retarding effect is associated with the presence of sodium ions. The same set delay can be obtained even with lower contents of the new waste-based additive (0.25–0.50 wt%), but the workability window tends to be narrower than that observed with the use of sodium enriched bentonite. The potable water filtration sludge can be a strong candidate in this application, with economical and environmental benefits.     

Study of the reactivity of cement/metakaolin binders at early age for specific use in steam cured precast concrete

The paper presents the results of a hydration study performed in order to explain the significant increase in compressive strength at one day of age observed on steam cured mortars when 25% by mass of cement was replaced with a metakaolin. Two CEM I 52.5R cements, differing in reactivity, and a metakaolin (MK) were used. By means of XRD and thermal analysis carried out on cement pastes, blended or not with MK, the main results showed that the improvement in strength at one day of age could be explained by the occurrence of a pozzolanic reaction due to MK, thermo-activated by the high curing temperature (55 °C). The pozzolanic reaction was observed through the consumption of calcium hydroxide and an increase in the amount of C–S–H and C–S–A–H hydrated phases. This change in the hydration product nature and amount was more pronounced when MK was combined with the less reactive cement, in agreement with the mechanical results on mortars. These results are of great importance for the concrete industry where the current trend is to decrease the clinker content in cements (1 ton of clinker = 1 ton of CO₂ released). In particular, the interesting mechanical performance at early ages can be helpful for precast concrete manufacturing.     

Flowing ability of the mortars formulated from self-compacting concretes incorporating rice husk ash

This paper presents the flowing ability of the mortars formulated from various self-compacting concretes (SCCs) incorporating rice husk ash (RHA). The mortars were produced with different RHA contents and water–binder (W/B) ratios, as used in their parent SCCs. The flowing ability of the mortars was determined with respect to the flow spread at various dosages of a polycarboxylate based high-range water reducer (HRWR). The effects of RHA, W/B ratio, and HRWR on the flowing ability of mortars were observed. The mortar flowing ability decreased with the higher RHA content and W/B ratio, but increased with the greater HRWR dosage. However, the excessive HRWR dosages were not conducive to the mortar flowing ability due to the segregation problem in the form of bleeding. The overall mortar flowing ability results were useful to examine the suitability of RHA, and to fix the HRWR dosages for different SCCs.     

Durability design and performance of self-consolidating lightweight concrete

In terms of the durability, the reduction in cement paste is crucial to both volume stability and long-term performance of concrete. The objective of this paper is to compare the performance of lightweight concrete under different w/cm ratio and different cement paste content. The slump and slump flow spread of fresh self-consolidating lightweight concrete (SCLWC) are designed to be within 230–270 and 550–650 mm, respectively. The test results indicate that the 91-day compressive strength of SCLWC is up to 56 MPa when cement content is 386 kg/m³ and water content is 150 kg/m³. If enough cement paste is used, then the less the paste amount and the denser the packing of aggregate, the higher the strength efficiency of cement and the electric resistance, and the lower the chloride ion penetrability capacity of SCLWC.     

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.     

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.     

Performance of limestone cement mortars in a high sulfates environment

With the aim of studying the influence of cement composition on resistance in high sulfates environment, standard mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 35% limestone (CEM II/B-LL – 32.5). The pore size distribution of the cement pastes was measured. The mortars were immersed in a 5% Na₂SO₄ solution at 20 °C for 1.5 years and the caused deterioration was been visually observed at a regular basis. Furthermore, the mortars expansion was being estimated by measuring the change of length. At the end of the experiment the compressive strength of the mortars was measured. The deterioration products of the mortars have been identified by means of X-ray diffraction, optical microscopy and environmental scanning electron microscopy. The limestone cement based mortar presented cracking that started at the age of 6 months and continued throughout the experiment. It also displayed high expansion after 250 days of immersion in a 5% Na₂SO₄ caused, as proved using the analytical techniques, by the formation of gypsum and ettringite. Concluding, the cement with 35% limestone did not perform as well as ordinary Portland cement under the most aggressive laboratory conditions. Hence, it is obvious that the addition of limestone in the cement leads to a totally different behaviour than Portland cement with respect to the resistance in high sulfates environment.     

Utilization of bagasse ash as a pozzolanic material in concrete

The physical properties of concrete containing ground bagasse ash (BA) including compressive strength, water permeability, and heat evolution, were investigated. Bagasse ash from a sugar factory was ground using a ball mill until the particles retained on a No. 325 sieve were less than 5wt%. They were then used as a replacement for Type I Portland cement at 10, 20, and 30wt% of binder. The water to binder (W/B) ratio and binder content of the concrete were held constant at 0.50 and 350 kg/m³, respectively.The results showed that, at the age of 28 days, the concrete samples containing 10–30% ground bagasse ash by weight of binder had greater compressive strengths than the control concrete (concrete without ground bagasse ash), while the water permeability was lower than the control concrete. Concrete containing 20% ground bagasse ash had the highest compressive strength at 113% of the control concrete. The water permeability of concrete decreased as the fractional replacement of ground bagasse ash was increased. For the heat evolution, the maximum temperature rise of concrete containing ground bagasse ash was lower than the control concrete. It was also found that the maximum temperature rise of the concrete was reduced 13, 23, and 33% as compared with the control concrete when the cement was replaced by ground bagasse ash at 10, 20, and 30wt% of binder, respectively. The results indicate that ground bagasse ash can be used as a pozzolanic material in concrete with an acceptable strength, lower heat evolution, and reduced water permeability with respect to the control concrete.     

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.