Days Of Water Curing Research Articles

Long-term strength and durability performance of eco-friendly concrete with supplementary cementitious materials

Research has shown that adding supplementary cementitious materials (SCMs), such as fly ash (FA) and slag (SL), to concrete improves its mechanical and durability properties up to certain limits. However, the long-term performance of concrete made with FA and SL is not fully known. This study investigates the impact of FA and SL on the long-term (up to 900 days) performance of concrete. The concrete specimens were made with six replacement percentages (0, 10, 20, 30, 45 and 60 by weight) of ordinary Portland cement (OPC). The short-term fresh and hardened properties of all concrete mixes were assessed after 14, 28, 60, and 90 days of water curing. After 120, 365, 730, and 900 days of water curing, the long-term performance was investigated for 100% OPC (control), 30% FA, and 30% SL concretes. At 28 days, no significant difference in strength development was observed for the concrete mixes containing up to 30% FA and 30% SL than the control concrete (100% OPC). In contrast, a remarkable enhancement in strength development was registered for all mixes containing up to 30% FA and 30% SL at 60 and 90 days of tests. Likewise, 30% FA and 30% SL showed the lowest porosity and water absorption than the control. The mechanical strength of concrete prepared with 30% FA and 30% SL gradually rises over time (from 14 to 900 days) compared to the control concrete. With increasing concrete age, a reduction in porosity and capillary water absorption was seen (up to 900 days).

Investigating the effect of Manufactured sand and Silica Fume on the properties of Concrete

In the present era, concrete is one of the most commonly used construction materials worldwide. Consequently, the demand for natural river sand is increasing. Since the mining of natural sand has already been outlawed by the government in many regions, now it is essential to look into sustainable materials to control natural sand extraction. Hence, manufactured sand (MS) has been shown in numerous studies to be a more practical and environmentally responsible alternative to river sand (RS), which is normally used in the production of concrete. At the same time, the cement industry produces tons of greenhouse gases into the atmosphere, affecting atmospheric conditions. Now, it’s time to look into a suitable replacement material for cement. To investigate the feasibility of using manufactured sand & silica fume in place of river sand and cement under normal climatic conditions fresh, mechanical and durability properties were conducted in the laboratory. Twelve samples of M30 grade cubes and cylinders at desired M sand percentages of 0, 20, 40, 60, 80, and 100 & 0% and 5% variation of silica fume with cement are included in this study as a comparison to the control mix. After 28 days of water curing, a random variation in the properties of concrete was observed in the samples. In this experimental study, SF represents Silica Fume, MS represents manufactured sand, RS represents river sand, FA represents Fine aggregates and CA represents Coarse aggregates.

Combined effect of fineness modulus and grading zones of fine aggregate on fresh properties and compressive strength of self compacted concrete

Self-compacted concrete (SCC) considered as a revolution progress in concrete technology due to its ability for flowing through forms, fusion with reinforcement, compact itself by its weight without using vibrators and economic advantages. This research aims to assess the fresh properties of SCC and study their effect on its compressive strength using different grading zones and different fineness modulus (F.M) of fine aggregate. The fineness modulus used in this study was (2.73, 2.82,2.9& 3.12) for different zones of grading (zone I, zone II& marginal zone(between zone I&II)) according to Iraqi standards (I.Q.S No.45/1984).Twelve mixes were prepared, each mix were tested in fresh state with slump, V-Funnel and L-Box tests, then 72 concrete cubes of (100*100*100) mm for different mixes were tested for compressive strength after 7 and 28 days of water curing. Results indicated that the combined effect of finenessmodulus and grading zone were clear on the passing ability and little effect of grading zone on flow ability and viscosity of fresh SCC properties. Compressive strength decreases with increasing F.M and no effect of grading zone for F.M higher than 2.90

The positive effects of power ultrasound on Portland cement pastes and mortars; a study of chemical shrinkage and mechanical performance

The influence of the direct application of power ultrasound (PUS) on the pore solution of Portland cement (PC) pastes was previously found by the authors to increase the aluminium concentration in the pore solution. The evidence of increasing the aluminate and carbonates in the pore solution was observed. In the present work, the effect of PUS on the rate and extent of PC hydration was followed by measuring the chemical shrinkage using an automated dilatometry method. Additionally, the compressive and flexural strength of the PC mortars were evaluated over 91 days. The results showed an increase in the rate of chemical shrinkage when both 26 and 132 kHz frequencies were applied to the cement paste for 2 min, soon after mixing. Sonicating at the higher acoustic power intensity of 26 kHz resulted in a higher rate of both compressive and flexural strength development for mortars over 91 days of curing in water. The addition of aggregates to the pre-sonicated paste was found to lead to 17% increase in the flexural strength of mortars at 28 days, indicating a possible modification of the paste-aggregate interface.

Mechanical and durability behaviour of fiber reinforced concrete

Fiber Reinforced Concrete (FRC) is broadly used in the construction of large buildings, industrial floors, and pavements due to the presence of exceptional mechanical and durable properties, having modest production cost. The impact of different types of fiber and environmental conditions on the strength and durability of ordinary concrete, such as steel fiber, polypropylene(PP) fiber, and natural palm tree fiber, varies. A variety of conventional material tests were performed to analyze the compressive strength and flexural properties. The experimental results showed that fiber stomping may take place at higher fiber volume fractions, resulting in mixing and casting issues. Based on the mechanical properties and anti-dry-shrinkage cracking resistance of FRC, the suitable fiber length and volume fractions were determined. In 28 days of water curing, adding small amounts of PP fiber can significantly increase compressive strength, flexural strength, and durability. However, in 6 months of wet-dry and heat-cool cycles, steel fiber performed better than PP fiber. The study also found that early shrinking of cracks decreases with an increase in fiber volume fraction, and no cracks are observed when a volume of 0.20% is used. These results can be used as a testimonial for the material proportion design of concrete.

Sustainability assessment of cement concrete modified with bagasse ash and calcite powder

The continued global expansion in the built environment has resulted in significant demand for cement as a building and construction material. However, carbon dioxide emissions from the cement manufacturing processes contribute significantly to global warming and climate change. This study evaluates the sustainability of cement concrete mixed with bagasse ash (BA) and calcite powder (CP). A binary mixture of BA (5–15%) and CP (5–15%) was used in a partial replacement level of cement using a 25 MPa concrete mix design. Slump was examined while compressive strengths were tested after 7–28 days of water curing. Embodied energy, embodied carbon dioxide emissions, and sustainability index of the mixed concrete were evaluated after 28 days using the carbon and energy inventory. The results showed a decrease in slump as the replacement of bagasse ash and calcite powder in the mixture increased. In addition, the compressive strength of the mixed concrete decreased slightly as the percentage replacement of BA and CP in the mix increased. However, at 15% BA and 15% CP replacement level, the ternary concrete mix attained the compressive strength of 25.53 MPa compared to 29.45 MPa obtained for the control sample after 28 days. In addition, the blended concrete resulted in lower embodied energy, embodied carbon dioxide emissions, and sustainability index than the control concrete, meaning that cement-based concrete modified with BA and CP is more sustainable than Portland cement concrete.

Experimental Investigation on Carbonation of Concrete Using SEM –EDX(Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDX) & Environmental Scanning Electron Microscope(ESEM) Analysis

The alkalinity of the concrete protects the reinforcing bars against corrosion, but the carbonation phenomenon accelerates the loss of their motionless coating, favouring corrosion start. Concrete that has been carbonated has a lower pH values which can lead to reinforcement corrosion. Reinforcement corrosion is the most common cause of reinforced concrete degradation Variables such as dimensional carbon dioxide in gress, duration of carbon dioxide ingress, grade of concrete, and CO2 volumetric concentration are all considered in this research. The specimens wereplaced in a chamber with a carbon dioxide gas supply after 28 days of water curing. The specimens were exposed to carbon dioxide for 145 hours and 290 hours, respectively, in a carbon dioxide chamber. The specimens were then cut at 1cm, 2cm, and 3cm intervals from the concrete surface. The powder from crushed concrete specimens was pulverised and sieved through a 90m sieve, with the powder collected as sample powder. In the present study an experimental investigation was conducted on concrete for determining the flexural strength and SEM- EDX & ESEM analysis. The specimens were tested after 28 days of curing as per determined time. The compressive strength, tensile strength and flexural strength of concrete is determined for the 7days,14 days and 28days curing.

New self-healing system for cracks repairing

Macrocapsules with an expanding mineral powder were set-up for sealing cracks into cementbased materials. The expanding mineral powder was composed of a commercial fast setting cement mortar, sodium polyacrylate and a commercial product used to produce sparkling water (based on sodium acid carbonate, malic acid and tartaric acid). An optimal proportioning of these components was determined as 10:1:1, respectively. These compounds were first mixed with polyethylene glycol and cast into cylindrical moulds. Then, the mix was heated at 230°C in an oven and the cylinders were demoulded thereafter. The obtained products could be delicately handled and were coated with an epoxy resin to produce waterproofed macrocapsules, while some uncoated cylinders were mixed with water and kept in closed containers for 14 days. Brazilian tests were performed on these hydrated cylinders to determine their indirect tensile strength. Finally, the coated macrocapsules were incorporated into mortar prisms, that were pre-cracked in three-point bending test after 14 days. The prisms were kept under water for 8 days and showed a sealing efficiency of 98.7% with a water flow of 3.8 g/min, which decreased to 3.5 g/min after 18 days of water curing. The same samples were stored 10 more days under water to reach an overall healing time of 28 days, after which they were subjected again to a three-point bending test to assess the recovery of the mechanical properties in flexion. The average recovered flexural strength was (10.6 ±4.5)%.

EVALUATION OF CURING TIME FOR MICRO CONCRETE MIXES CONTAINING SILICA FUME, NANO-SILICA AND FLY ASH

Within the scope of the study, research on the use of silica fume (SF), nano silica (NS) and fly ash (FA) together or separately in the production of micro concrete is presented. It is aimed to examine the changes in mechanical properties because of water and air curing in mixtures produced using SF, FA, and NS. While cement dosage and water/binder ratio in the mixtures were chosen as 670 kg/m3 and 0.53 respectively, the amount of SF, FA and NS was limited to 150 kg/m3 in total. In the study, samples were produced using 40x40x160 mm prism molds. All samples were divided into two different groups after 7 days of water curing and water (1st group) and air (2nd group) were applied up to 56 days. Flexural and compressive strength tests were performed on the water and air cured specimens for 7-56 days and 28-56 days, respectively. In addition, the porosity and unit volume weight values of the samples were examined. The results show that both flexural and compressive strengths of micro concretes increased after 28 days thanks to water curing.

Effect of Human Hair Fibers on the Performance of Concrete Incorporating High Dosage of Silica Fume

Sustainable development in structural materials is currently getting attention all around the world. Solid waste, building and demolition waste, natural resources, and their reuse are the most obvious strategies for achieving sustainability in the construction industry. Solid waste human hair fiber (HHF) with a diameter of 70 µm and a length of 30–40 mm is used as a fiber, having a dosage of 0%, 1%, 1.5%, 2%, 3%, 4%, and 5%, while silica fume (SF) with a dosage of 0%, 5%, 10%, 15%, 20%, 25%, and 30% is used as a cement substitute. A drop of 50 mm to 75 mm slump was witnessed for the water–cement ratio used in the M20 mix design of concrete. The concrete’s mechanical properties, such as compressive, split tensile, and flexural strength, were determined after 28 days of water curing. The concept of the response surface methodology (RSM) for optimizing human hair fiber concrete (HHFC) and SF substitution was used, which was validated by the polynomial work expectation. The model is statistically significant when the fluctuation of the analysis of variance (ANOVA) is analyzed using a p-value with a significance level of 0.05. The test results showed that the use of 2% human hair as fiber and 15% SF as a cementitious additive or cement replacement considerably improved the strength of concrete. The compressive, flexural, and split tensile strengths of HHFC improved by 14%, 8%, and 7%, respectively, which shows the significance of human hair and the partial replacement of cement with SF. Moreover, SEM analysis was carried out to study the microstructure of the concrete matrix.

Corrosion prevention of steel rebar embedded in the cement mortar under accelerated conditions: Combined effects of phosphate and chloride ions

The present work focuses on the role of different amounts i.e. 0.295 and 2.95 kg/m3 ammonium phosphate monobasic (NH4H2PO4: APM) inhibitor and 1.2 kg/m3 NaCl as admixtures in cement mortar under wetting–drying accelerated condition to mitigate the corrosion of steel rebar. The results show that phosphate ions (from APM) react with NaCl and ordinary Portland cement (OPC) constituents to form Ca3(PO4)2 and Ca5(PO4)3Cl as hydration products, which led to make the cement mortar matrix dense and compact, and thus, improved the compressive strength after 28 days of water curing. Consequently, the phosphate ions in the cement mortar initiate the oxidation of embedded steel rebars immersed in 3.5 wt. % NaCl solution due to the formation of Fe(H2PO4)2, and FeHPO4 as intermediate. These could be transformed into stable and protective tertiary iron phosphate (FePO4) if optimum amount of phosphate ions is present but in the case of 0.295 kg/m3 APM, mostly phosphate ions consumed in the formation of Ca3(PO4)2 and Ca5(PO4)3Cl. Therefore, this sample became vulnerable to corrosion. On the other hand, 2.95 kg/m3 APM, the phosphate ions are significant and, thus, it helps to properly form the Ca3(PO4)2, Ca5(PO4)3Cl, FePO4 and maghemite (γ-Fe2O3).

Is Cement Paste Modified with Carbon Nanomaterials Capable of Self-Repair after a Fire?

Abstract This manuscript presents preliminary results on the cement paste potential, with and without carbon nanomaterials, to heal high-temperature cracks. Cement paste beams were subjected to thermal loading of 200°C and 400°C after 28 days of water curing. High temperature caused the formation of microcrack networks on the specimen’s surface. Self-healing was achieved by exposing the cracked samples to cyclic water immersion. The efficiency of the process was evaluated based on the crack closure and mechanical properties recovery after 24 days. The results indicated a distinct dependence of the healing on the loading temperature. Carbon nanotubes had a positive effect on self-repair efficiency.

Bio-based aggregate in the production of advanced thermal-insulating concrete with improved acoustic performance

Concrete is the most utilized man-made building material and its global production reaching 25 billion tons per year represents a huge burden on our environment. Unsurprisingly, a lot of effort is dedicated to searching for suitable replacing materials of concrete constituents, e.g. of mineral aggregate that usually forms 70–80 vol% of fresh concrete mix, not only to reduce the depletion of our natural resources, but, at the same time, to improve some of the concrete properties. For example, dense building materials are not very effective in acoustic-insulation performance. In this context, renewable resources can provide a possible solution in the preparation of advanced concrete composites that will help to reduce noise originating in high populated urban and/or industrialized areas. This paper is focused on the application of carbonized lightweight bio-based aggregate (BA), having about 63 % lower thermal conductivity compared to the traditional ones, in the manufacturing of lightweight concretes which, related to BA quantity in mixes, dispose with considerably mitigated thermal transport properties and enhanced acoustic-insulation function. Traditional dense aggregate was replaced with the bio-based alternative in the amount of 0–100 vol% and the batch water content was adjusted to keep similar consistency (class S4) of fresh concrete mixes. After 28 days of water curing, the development of dry bulk density, open porosity, flexural and compressive strengths as well as thermal and acoustic performance in the dependence on bio-based aggregate content were determined on hardened specimens. Experimental investigation revealed significant lightening effect of BA particles having a honeycomb-like porous structure and thus promoting the high thermal and acoustic performance of developed concretes. Accordingly, hardened concrete samples with alternative aggregate content only showed 7.5 times lower thermal transport and about 16.2 % improved acoustic performance compared with ordinary dense concrete. In addition, lower BA dosages (up to 50 vol%) allowed to produce concretes disposing sufficient strength parameters – average flexural strength about 6.5 MPa and compressive strength about 27.0 MPa maintaining their usage for structural purposes. Furthermore, bio-based aggregates are sorted among renewable resources that may mitigate environmental impacts connected with the quarrying of traditional filling materials, and thus contribute to higher sustainability of concrete production.

Fired clay brick waste as low cost and eco-friendly pozzolana active filler in gypsum-based binders

A broader utilization of calcined gypsum in external applications remains limited mainly due to its high solubility in water. This drawback can be improved by combining it with supplementary cementitious materials and an activator of pozzolanic reactions (cement or lime). This paper aims to explore the feasibility of utilizing non-conventionally used fired clay brick waste, a by-product from brick production, to design gypsum-based binders with improved water resistance. A comprehensive study of the system consisting of calcined gypsum, fired clay brick waste, and lime was done from a microscopic (mineral composition, porosity development, and morphology) to macroscopic (basic physical and mechanical properties) point of view up to 90 days of age. Additionally, a simplified environmental study was conducted using the Life Cycle Assessment method. Amorphous phase and ettringite were the main hydration products. The mechanical tests revealed that the pozzolanic reactions caused by the addition of fired clay brick waste were delayed, which was reflected by a slow increase in strength within the studied period. Contrary to the reference binders, the compressive strength of the samples containing the lowest percentage of fired clay brick waste provided the most promising results even after 90 days of water curing. Considering that the newly designed ternary binders are prepared from low-cost and eco-friendly pozzolana active waste, the results presented in this study could help eliminate the disposal of fired clay brick waste and convert it into useful binder material suitable for green building rendering and restoration work of historical buildings.

An Experimental Study on Electrical Properties of Self-Sensing Mortar

Self-sensing cementitious composites are a combination of conventional materials used in the construction industry along with any type of electrically conductive filler material. Research has already been carried out with various types of conductive fillers incorporated into cement mortars to develop a self-sensing material. Carbon fibres have been used as conductive fillers in the past, which is uneconomical. In order to overcome this drawback, brass fibres have been introduced. This study concentrates on the behaviour of self-sensing mortar under two different curing conditions, including air and water curing. The main aim of this paper is to determine the self-sensing ability of various types of smart mortars. For this purpose, an experimental study was carried out, with the addition of various brass fibres of 0.10%, 0.15%, 0.20%, 0.25%, and 0.30% by volume, to determine the electrical properties of cementitious mortar. In addition, different combinations of brass and carbon fibres were considered, such as 95% brass fibre with 5% carbon fibre, 90% brass fibre with 10% carbon fibre, and 85% brass fibre with 15% carbon fibre by volume, to determine the piezoresistive behaviour. A fractional change in electrical resistance was determined for all the mortar cubes. A fractional change in electrical resistance (fcr) is defined as the change in its electrical resistance with respect to its initial resistance (ΔR/R). Additionally, the temperature effects on self-sensing mortar under compressive loading were observed for various temperatures from room temperature to 800 °C (at room temperature, 200 °C, 400 °C, 600 °C, and 800 °C). It was observed that the addition of brass fibre to the cement mortar as an electrically conductive filler improved the self-sensing ability of the mortar. After 28 days of water curing, when compared to conventional mortar, the percentage increase in change in electrical resistance (fcr) was observed to be 26.00%, 26.87%, 27.87%, 38.55%, and 35.00% for 0.10%, 0.15%, 0.20%, 0.25%, and 0.30% addition of brass fibres, respectively. When the smart mortar was exposed to elevated temperatures, the compressive strength of the mortar was reduced. Additionally, the fractional change in electrical resistance values was also reduced with the increase in temperature. In addition to this, the self-sensing ability of smart mortars showed improved performance in water curing rather than in air-cured mortars. Compressive strengths, stress, strain, and change in electrical resistance (fcr) values were determined in this study. Finally, microstructural analysis was also performed to determine the surface topography and chemical composition of the mortar with different fibre combinations.

Short-term and long-term behavior of RC beams strengthened by galvanized steel mesh laminate

Steel reinforced polymers (SRP) are useful in a wide range of applications, including strengthening of existing reinforced concrete (RC) structures, due to their numerous advantages like high strength, low maintenance, light weight and low cost. As such, galvanized steel mesh (GSM) has emerged as an option in the strengthening of RC structures. Although numerous studies were performed on GSM strengthened RC beams, the durability of such strengthening systems is yet to be fully understood. This paper presents an experimental and numerical study to investigate the strengthening effect of GSM on RC beams as well as the time-depended behavior of RC beams with and without strengthening. Reinforced concrete beams without strengthening were used as control beams. For the strengthened beams, both high cord density galvanized steel mesh (HSM) and medium cord density galvanized steel mesh (MSM) were used after which the beams were exposed to Qatar atmospheric environment for different periods of time following 28 days of water curing. Finite element analyses using ABAQUS software were conducted to predict the mechanical behavior of the RC beams with and without strengthening. The results showed an improvement ranging from 46% ∼ 57% in the ultimate load of GSM strengthened beams, with a higher initial cracking load ranging from 3% ∼ 35% when compared to the unstrengthened beams. On the other hand, the time-dependent effect of the concrete has limited influence on the initial cracking load of both systems (before and after strengthening) while the ultimate load increased gradually with time due to the strength development of concrete. The results obtained from this study are useful in improving the design, construction, and maintenance of RC beams strengthened with GSM laminates.

Mechanical Behaviour of Concrete Containing Crumb Rubber as Partial Fine Aggregates Replacement

Nowadays, the waste tires became a critical issue for many countries as the transportation industries increase around the world. Normally, the worn-out tires will be discarded and become an environmental threat or resourceful end product depending on the waste management of the country. Thus, the aim of this study is to investigate the effect of crumb rubber as partial replacement of fine aggregates in compressive and tensile strength of concrete. Based on the mechanical behaviour, the optimum content of crumb rubber as partial fine aggregates replacement in concrete is determined. The size of crumb rubber used in this study was between 2 mm and 3 mm with 5% to 15% replacements. The targeted strength of concrete at 28th days is 35 MPa with 0.32 water to cement ratio. The slump test was conducted to measure the workability of the mix. 24 concrete cubes with dimension of 150 mm x 150 mm x 150 mm were tested for compressive strength after 7 and 28 days of water curing. In addition, 12 cylinders (100 mm x 200 mm) were prepared for tensile strength test. Based on the results of compressive and tensile strength, generally both strengths decreased as the percentages of replacement increased. However, for 5% and 10% replacement, the targeted strength is still achieved. Hence, it can be concluded that, 10% of rubber crumb is the optimum percentages to be partial replacement of fine aggregates in concrete.

Carbon sequestration in engineered lightweight foamed mortar – Effect on rheology, mechanical and durability properties

Enhancing carbon sequestration in Portland cement-based foamed mortar is a potential means to reduce carbon emissions associated with lightweight building components. This research aims to investigate the influence of biochar, prepared from wood waste, in enhancing carbon sequestration in foamed mortar of three target densities – 1150 kg/m3 and 1300 kg/m3 and 1450 kg/m3 respectively through accelerated carbonation (CO2 concentration of 2%) technique. Effect of biochar on rheology, and influence of carbonation on micro-structure, compressive strength, water absorption and shrinkage are investigated. Based on thermogravimetry analysis, carbon dioxide uptake of 26.80% and 30% by mass of cement are achieved in foamed mortar containing biochar, silica fume and fly ash after 7 days and 28 days respectively, which is higher by 3% compared to control (without biochar). Adding biochar to replace 3% by mass of fly ash (density of 1150 kg/m3) and 20% by mass of silica fume (density 1450 kg/m3) improves the workability of foamed mortar mixtures, evident from the 32% and 44% reduction in yield stress up to 35 min from the time of wet mixing. For density groups of 1300 kg/m3 and 1450 kg/m3, addition of biochar reduces water-accessible porosity by 2 – 3%, leading to 17% and 23% higher compressive strength compared to the controls after 28 days of water curing. After carbonation biochar-foamed mortars retain 20–38% higher strength than the respective controls, although reduction in strength by 40 – 60% compared to water curing is observed, ascribed to degradation of hydration products during prolonged carbonation. Addition of biochar results in 10–12% higher shrinkage under an air-drying regime, while it reduces chemical shrinkage associated with carbonation by 15–20% than control. Overall, this study demonstrates a promising potential for developing biochar-enhanced low-carbon lightweight building products.

Effect of Nano-SiO2/PVA Fiber on Sulfate Resistance of Cement Mortar Containing High-Volume Fly Ash.

Sulfate resistance of high-volume fly ash/cement mortars hybrid containing 0~1.5 wt.% of nano-silica (Nano-SiO2, NS) and 0~1.0 vol.% of polyvinyl alcohol (PVA) fibers was investigated in this study. Fly ash was replaced with Portland cement at levels of 60% by weight. The resistance to sulfate attack was investigated by exposing the mortars to 10 wt.% sodium sulfate (Na2SO4) solutions for 72 days, after which change in mass, compressive, and flexural strengths were determined. For comparison, the compressive and flexural strengths of cement mortar after 100 days of curing in water were also investigated. Microstructural deteriorations caused by sulfate attack were analyzed by using scanning electron microscope (SEM). The test results showed that the combination of NS and PVA fibers was effective in enhancing the mechanical properties and the resistance to sulfate attack. After 28 days curing, the hybrid addition of 1.5 wt.% NS and 1.0 vol.% PVA fibers increased the flexural strength by 90% over the control one without NS and PVA fiber. Moreover, regardless of PVA fibers content, due to the crystal nucleus and pore-filling effects, the adding of 0.5 wt.% NS increased the compressive strength by 67.1~118.2%. Chemical reaction took place between fly ash and Na2SO4 as no un-hydration particles could be observed in the samples immersed in Na2SO4 solutions for 72 days, while a lot of un-hydration fly ash particles could be found in the SEM image of mortar after 100 days curing in water. The chemical reaction production could increase the adhesive property and fill the pores of cement mortar. As a result, the compressive and flexural strengths of cement mortars after immersed in Na2SO4 solution for 72 days, were much higher than that after 28 days curing. Moreover, the compressive strength of mortars incorporating 1.0~1.5 wt.% NS was even higher than that after 100 days curing in water, indicating the combination of Nano-SiO2/PVA fiber is effective in enhancing the resistance to sulfate attack.

Chemical shrinkage of paste and mortar containing limestone fines

The effect of including limestone fine (LF) on the chemical shrinkage of cement paste and mortar is investigated. The cement was partially replaced with 0 to 20% (by weight) with LF. The water to cementitious material (CM) ratio was maintained at 0.45. In the mortar mixes, the proportion of sand (S) to CM was 1:2. In addition to the chemical shrinkage test, compressive strength and density of specimens were determined. The chemical shrinkage data were collected up to 28 days. However, for compressive strength and density, testing continued up to 90 days of water curing. There appears to be an increase in chemical shrinkage between 10 and 15% limestone for both paste and mortar mixes. The trend appears to be similar for the compressive and density results.