Presence Of Superplasticizer Research Articles

Effect of Different Concentration of CO2 Gas Injected into Fresh Cement Paste Along with the Addition of Superplasticizer on the Mechanical Properties of Cement

This paper focused on examining the impact of injecting varying concentrations of carbon dioxide (CO2) gas on the mechanical characteristics of both the fresh and hardened states of cement paste. This study also considered the influence of the presence or absence of polycarboxylate superplasticizer in cement mixture on these properties. Many researchers discovered the benefit of CO2 gas utilization in cement mixture to accelerate the early strength of cement or concrete hydration by its carbonation that form calcium carbonate (CaCO3). The application method is to directly inject CO2 gas in a curing chamber for air-curing of precast concrete. Alternatively, carbonated water is mixed with cement during concrete mixing. However, the use of CO2 gas does not significantly improve the 28-day strength of concrete. This study explores how to improve the carbonation impact on mechanical properties of cement paste and apply it to ground improvement. In this study, the method adopted is direct injection of CO2 gas during cement slurry mixing with different injection duration. The influence of CO2 in the presence of superplasticizer (SP) in cement slurry was also studied as SP is generally used for grouting. The results showed that the carbonation of cement paste with additional of superplasticizer significantly affect its flow, viscosity and bleeding properties. Unlike samples with SP addition, the samples without SP addition showed higher compressive strength after 28 days of curing up to certain CO2 injection time. For all CO2 gas injection time, smaller porosity rates were observed for 7-day cured samples with SP addition compared to those without SP addition. This is due to accelerated carbonation due to SP presence in cement mixture. From the results, the optimum of CO2 gas injection time for one liter mixture of cement paste to improve its compressive strength (up to 123% increase) have been discovered. It can be inferred that the addition of superplasticizer in cement slurry reduces the amount of CO32- ions and Ca2+ ions during carbonation process of cement hydration products, which are strongly related to the pH level in pore solution. These ions play a significant roles in determining the mechanical properties of cement slurry.

ВЛИЯНИЕ ПЛАСТИФИКАТОРА НА ПРОЦЕССЫ ПЕРЕКРИСТАЛЛИЗАЦИИ ПРИ ТВЕРДЕНИИ ДВЕНАДЦАТИКАЛЬЦИЕВОГО СЕМИАЛЮМИНАТА КАЛЬЦИЯ

The mechanism of structure formation during hydration of duodecalcium semialuminate in the presence of plasticizer is considered. The purpose of the study was to determine the influence of polycarboxylate-based plasticizer on the formation and morphology of the hydrate phases formed. The object of the study was the mineral duodecalcium semialuminate 12CaO-7Al2O3 of stable α-form, having cubic syngony and plasticizer on polycarboxylate basis. The structure of cement stone was studied using X-ray phase and electron microscopic analysis. The mechanism of structure formation during hydration of duodecalcium semialuminate 12CaO∙7Al2O3 in the presence of plasticizer is presented, which consists in the formation of finely dispersed poorly crystallized hexagonal crystals of calcium hydroaluminate. The presence of superplasticizer in the composition of hydrated calcium aluminate slows down the nucleation and growth of crystalline hydrates due to the film formed on the surface of the interface between liquid and solid phases, creating a structural and mechanical barrier, which leads to slower saturation of the liquid phase, but promotes the formation of a greater number of crystallization centers and simultaneous growth of small crystals of both hexagonal and cubic habitus.

Effect of competitive adsorption between specialty admixtures and superplasticizer on structural build-up and hardened property of mortar phase of ultra-high-performance concrete

This study aims to enhance structural build-up of ultra-high-performance concrete (UHPC) without influencing the initial flowability, which is critical in repair applications (e.g., use of UHPC in thin bonded overlays for bridge deck rehabilitation). Specialty admixtures, such as a viscosity-modifying admixture (VMA), have been used to enhance the structural build-up at rest. However, the use of specialty admixtures can increase superplasticizer (SP) demand to maintain proper flowability; the synergistic effect of these admixtures on structural build-up is not well understood as the coupled admixture content can reverse the net effect on yield stress, viscosity, and thixotropy. In this study, VMAs including welan gum (WG), diutan gum (DG), and cellulose ether (CE) were used. Styrene-butadiene rubber (SBR) and acrylic ester (AE) latex polymers (LPs) that can enhance structural build-up and bond strength were also incorporated. The competitive adsorption between these specialty admixtures and SP and its effect on structural build-up, early-age hydration, compressive and pull-off strengths, porosity and entrapped air content of UHPC mortar (i.e., without fiber) were systematically investigated. Test results indicated that the incorporation of anionic WG and DG that exhibited high competitive adsorption with SP led to a 275%–450% enhancement in structural build-up despite the 55%–135% increase of SP demand. Such increase was limited to 130% when using CE, SBR, or AE that cannot effectively adsorb onto cement particles in the presence of SP. This was because the high competitive adsorption between specialty admixtures and SP strengthened the particle flocculation and promoted the cement hydration in the first hour; the latter resulted in 20%–40% enhancement in non-reversible component of structural build-up. Furthermore, the use of LP at low and moderate dosages secured high bond strength to normal strength mortar despite 8%–33% decrease in compressive strength given the increased capillary porosity. The use of VMAs increased the entrapped air and resulting 5%–15% lower compressive strength, while the bond strength was not influenced.

Effect of Excessive Bleeding on the Properties of Cement Mortar

The bleeding of cementitious materials corresponds to the settlement of the granular skeleton accompanied by the accumulation of water at the surface (bleed water). Part of this water (internal bleeding) remains trapped under the aggregates (sand or gravel) or the reinforcements. The excess of this trapped water can weaken the bond between the cementitious matrix and the aggregates (or the reinforcements), which affects the mechanical performance and durability of the material. This study aims to investigate the effect of excessive bleeding induced by superplasticizer on the properties of mortars. For this, a study of cement paste bleeding in the presence of superplasticizer was carried out. The effects of the water-to-cement ratio (w/c) and the superplasticizer (SP) dosage on this bleeding have been characterized. Then, the influence of the proportion of sand on the bleeding was examined by varying the sand/cement (s/c) ratio. The water trapped by sand (internal bleeding) was determined by the difference between the external bleeding on the cement paste and the external bleeding on the corresponding mortar. The results show that the internal bleeding increases with the s/c ratio and the SP dosage, until it reaches a plateau. The effect of the internal bleeding on the mechanical properties and the porosity of the mortar were then examined. Microscopic observations were made to assess the quality of the paste/sand bond. The results showed that the internal bleeding causes a degradation of the paste/sand bond (a more porous bond), resulting in a decrease in the mechanical strength (by 30% for compressive strength and 25% for flexural strength) of the hardened mortar.

INFLUENCE OF SUPERPLASTICIZERS МС POWER FLOW 3100 ON CALCIUM SULPHATE DIHYDRATE TECHNICAL PARAMETERS

In recent years, there has been a decrease in gypsum products demand. Theimproving of gypsum binders properties can help to expand the scope of gypsum binders and, as aresult, increase gypsum products demand. The structure of the gypsum binder is the carrier of itsproperties. Studying the relationship between structure and properties is the way to directedelimination of disadvantages. One of the ways to eliminate the disadvantages is the modification ofsurfactants and nanoparticles, which affect and allow to control the hydration process. Therefore,the aim of the research is to study the effect of superplasticizer MC Powerflow 3100 on themicrostructure. physical and technical properties of calcium dihydrate formed during the hardeningof gypsum binder. The increase in the strength of gypsum binder at the compression of 77 percentand the bending strength of 17.6 percent was received during the research. Alsow the water-gypsumratio was reduced by 10 percent and the curing time was reduced: beginning from 5 to 2.5 minutes,end from 12 to 8 minutes. It was also found that the presence of the superplasticizer MC Plaflow 3100in the curing system of gypsum binder changes the process of hardening and crystal formation. Itaffects on the morphology of gypsum dihydrate crystals. To study the effect of the superplasticizer onthe morphology of gypsum dihydrate crystals, the crystals were grown in the presence ofsuperplasticizer MC Powerflow 3100 by the method of counter growth. When superplasticizer MCPowerflow 3100 is added to the solution, the thickening of crystals occurs and alsow their doublingwith the formation of dendritic crystals form. The performed researches can be the basis for thedirected management of material structure for the purpose of receiving the new improved indicatorsof gypsum binders properties that in turn will allow to expand scope of application of this material.

Resting time effect on the rheological behavior of cement paste in presence of superplasticizer

Rheology has been widely used to describe the flow properties of fresh cement-based suspensions. Nevertheless, the effect of early hydration product formation on rheology, and the effect of shear on breaking of hydration bonds is not fully understood. Therefore, the characterization of the time-dependency of rheology has become necessary to predict precisely the behavior of concrete during placement. In this paper, variations in the resting time in between rheological tests were imposed to evaluate the effects on the development of internal structure of the mixture using different dispersing agents. Increasing resting time in between measurements mainly enhances viscosity, but the magnitude seems strongly dependent on the dispersant used. However, the effect of the employed procedure, as two procedures were evaluated, seems to have a stronger influence on the time-evolution of the rheological properties than changing the resting time in between measurements.

Influence of Lime and Marble powder Waste on the Strength Activity Index of Self Compacting Mortar and Concrete

Void free mass, congested reinforcement, reduced section, and surface finishes are the present demand in the construction sector that can be fulfilled using Self Compacting Concrete (SCC). It flows under self-weight and develops a homogeneous dense mass of concrete without external energy (Vibration). The research described in this research examined the making of SCC with readily available materials. The most crucial distinction is the presence of filler material and small aggregate size in the SCC mixture. To obtain the benefit of filler material, reduced cement content, improve workability and strength in SCC, two fillers selected from a group of natural inert by-product, limestone powder (LP), and marble powder (MP). For this purpose, mortar cube prepared as per BS 3892 with two fillers, LP and MP by 10%, 15%, and 20% of replacement with a different combination. Present work also investigates the pozzolanic and filler effect of partial replacement in mortars by strength activity index (SAI), also tried to develop the relationship between fresh SCC slump flow and V-flow spread time. The observed value in the SAI test for the sixteen samples of a mineral filler of 10%,15%, and 20% replacement compared with a normal mix, all samples have the value lower than the control mix of 80% as per BS 3892. It is due to the effect of the filler on the microstructure and the presence of superplasticizer. From these results, it is concluded that filler, LP, and MP does not contribute to pozzolanic reaction, and it is still unhydrated at the age of 28 days.

Effect of recycled fine aggregates on performance of Reactive Powder Concrete

Reactive Powder Concrete (RPC) is a special type of concrete in which traditional coarse aggregates are replaced by fine sand. Its main ingredients include a high percentage of Portland cement, a very low water-to-binder ratio, and the presence of super plasticizer, grey sand and silica fume. The main purpose of this research was to evaluate the performance of RPC produced by replacing the natural fine aggregates (grey sand) with recycled fine aggregates under varying curing conditions. Various properties including compressive strength, flexural strength, tensile strength, sorptivity, water absorption, electrical resistivity, sulphate resistance and resistance against marine environment were studied. Two types of recycled fine aggregates were used; one was obtained from demolished normal strength concrete and second was obtained from demolished RPC. It was found that the compressive strength of all tested samples increased when cured at 90 °C for 48 h, as compared to the samples kept under normal curing conditions. Mechanical properties of RPC prepared with recycled aggregates increased up to 50% replacement, while durability performance gradually reduced with an increase in the recycled aggregate content, but within reasonable limits.

Hydration properties of fly ash blended cement in presence of superplasticizer

Hydration of 15% Fly ash-OPC has been studied in presence of 0.4 wt% superplasticizer by using different techniques such as setting time, X-ray diffraction, FTIR spectroscopic and SEM studies. Compressive strength measurements were also made at different time interval. It was found that in presence of Fly ash, early strength is decreased. Whereas 28 days strength in presence of superplasticizer was highest. This could be due to morphological changes.

Influence of mixture composition on fresh concrete workability for ballastless track slabs

There are several factors that affect the fresh concrete workability: water demand and composition of Portland cement, properties of fine and coarse aggregates, presence of superplasticizer and others admixtures, etc. Influence of quantity and fineness of ground quartz additives as well as polycarboxylate-based superplasticizer amount on workability of fresh concrete was studied in the paper. The properties of fresh mixture (slump) and hardened concrete (compressive strength at the age of 24 hours, 28 and 360 days) were estimated. Enhancing the fresh concrete workability using fine ground quartz sand was stated. Savings of superplasticizer per 1 m3 of slab concrete and 1 km of the ballastless track were calculated.

Behavior of hybrid concrete beams with waste rubber

The studies on the applications of waste materials in concrete have been increased in Iraq since 2003. In this research, rubber wastes that resulting from scrapped tires was added to concrete mix with presence of superplasticizer. The mechanical properties of concrete and workability of concrete mixes were studied. The used rubber were ranging in size from (2-4) mm with addition percentages of (0.1% and 0.2%) by volume of concrete. The results of mechanical properties of concrete show that rubber enhance the ductility, and compressive and tensile strength compared to concrete without it. Also, the flexural behavior of hybrid strength concrete beams (due to using rubber at the bottom or top layer of section) was investigated. The rubber concrete located at bottom layer gives higher values of ultimate loads and deflections compared to the beam with top layer. A similar response to fiber concrete beam (all section contains 0.1% rubber) was recognized. Finite element modeling in three dimensions was carried for the tested beams using ABAQUS software. The ultimate loads and deflection obtained from experimental and finite elements are in good agreements with average difference of 8% in ultimate load and 20% in ultimate deflection.

Performance evaluation of sustainable high strength mortars incorporating high volume waste glass as binder

This study investigates the performance of sustainable high strength mortars incorporating recycled waste glass as a supplementary cementitious material (SCM) to replace cement from low (10%) to high (60%) replacement ratios, while mortars with conventional mix design are used as reference. The addition of the recycled waste glass significantly improves the slump-flow of fresh mortars in the presence of superplasticizer (SP). The increase of the recycled waste glass dosage contributes to the longer initial and final setting time compared to the plain cement sample. The high volume recycled waste glass containing sample shows an obvious delay of hydration compared with others incorporating the same amount of SP. The high strength series samples containing various contents of recycled waste glass show similar total gel porosity, but a significant increase of gel porosity was observed in the normal strength series samples containing recycled waste glass. From the SEM images, it can be identified that high dosage recycled waste glass-containing high strength mortars show a denser microstructure compared to the plain sample. The higher mesopore volume introduces higher drying shrinkage in sustainable mortars. The mechanical performance tests show that sustainable high strength mortars containing 60% recycled waste glass can achieve a satisfactory strength (99 MPa) compared to the plain cement sample (115 MPa).

Evaluate the influence of starch on earth/hemp or flax straws mixtures properties in presence of superplasticizer

In this paper, we study the influence of two types of starch on earth hemp or flax straw mixtures at fresh and hardened states. The main goal is to propose new non-load bearing earthen for indoor. The mass percentage of starch/binder (S/B) in mixtures was fixed at 1% of mass. The VEBE consistometer test has been used to fix a similar consistency between mixtures. The targeted workability has to allow an easy introduction of materials in the moulds. Adding both of starch has shown a positive effect on mixtures workability at the fresh state and mechanical resistances at the hardened state. At hardened state, mechanical and thermal-acoustic performances have been measured on laboratory samples and blocks at real scale. Results have shown a significant effect of starch on mechanical strengths.

Combined Influence of Opoka and Slag on Cement Properties in Presence of Superplasticizer

The influence of the milled opoka of Penza field and blast-furnace slag with the polycarboxylate superplasticizer present on the properties of mortar component of the concrete based on blended cement, including Portland cement, fly ash, blast-furnace slag, silica fume, and microquartz has been investigated. Some equations for the dependency of water requirement of the cement mortar component, as well as of its strength with various values of time on proportion of superplasticizer and components of blended binder have been developed. It has been shown that the introduction of opoka increases the water requirement of the mix, insignificantly decreasing the strength, when proportioned up to 15%. The detrimental effect of opoka on the strength considerably reduces with higher superplasticizer content and lower water-to-cement ratio.

Variations of Yield Stress of Fresh Cement Pastes in the Presence of Superplasticizer Highlighted by a Hydration Index

AbstractThe rheological properties of fresh cement pastes (FCPs) in the presence of superplasticizer were systematically investigated in this study where influential factors such as mix proportion ...

Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste

In this experimental study, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were dispersed by intensive sonication in water in the presence of superplasticizer and subsequently mixed with Portland cement with water/ cement ratios varying between 0.3 and 0.4. The autogenous shrinkage in the fresh stage was investigated. The CNTs and CNFs were characterized by high resolution scanning electron microscopy (SEM) and the hydrated pastes were studied by X-ray diffraction and SEM. The results showed a reduction of the autogenous shrinkage by 50% for pastes containing small amounts (0.01 wt%) of nanomaterials. Higher additions appeared to be less effective. The highest reduction of shrinkage was observed for carbon nanofibers which were long, rather straight and had diameters of around 200 nm. The result showed that the addition of nanomaterials accelerated the hydration processes especially in the early stages of hydration. The effect was the most pronounced in the case of functionalized nanotubes. The proposed mechanism resulting in the reduction of the autogenous shrinkage was a combination of nano-reinforcing effects, alterations of hydration and microstructure of the hydrated matrix.

Dispersion of Multi-Walled Carbon Nanotubes in Portland Cement Concrete Using Ultra-Sonication and Polycarboxylic Based Superplasticizer

The potential properties of carbon nanotube-cement based materials strongly depend on the dispersion of carbon nanotubes (CNTs) within the cement matrix and the bonding between CNTs and the hydrated cement. The homogeneous dispersion of CNTs in the cement matrix yet is one of the main challenges due to strong van der Waals forces between nanotubes. In this study, a polycarboxylic ether based superplasticizer and ultra-sonication technique was used for dispersion of multi-walled carbon nanotubes (MWCNTs). Portland cement concrete specimens with different concentrations of MWCNTs (0.04 and 0.1 % by the weight of cement), with and without the presence of superplasticizer were investigated. Compressive strength test results revealed a significant improvement in mechanical properties of sample containing 0.1 % MWCNTs and 0.2 % superplasticizer. Moreover, field emission scanning electron microscopy (FESEM) images of fractured surfaces of hardened specimens showed a good dispersion of MWCNTs within the cement matrix. This method was developed to facilitate the uniform dispersion of MWCNTs in the cementitious concrete for better reinforcement in nanoscale and mechanical properties enhancement by transfer of load between the nanotubes and matrix.

The Influence of Chosen Factors on the Rheological Properties of Cement Paste

Rheological investigations were conducted into cement paste made of various cement types (CEM I 42.5 R, CEM II/B-S 42.5 R, CEM III/A 32.5 N LH/HSR/NA), with and without superplasticizer. The tests were performed at 15°C, 20°C and 25°C, for one hour. Rheological parameters (yield value and plastic viscosity) were designated according to the Bingham model. The influences of hydration time, the presence of superplasticizer and of temperature on the occurrence of the thixotropy phenomenon in cement paste were identified. The thixotropy was analysed by measuring hysteresis loops surfaces using a numerical integral method.

Effect of Bentonite on the Rheological Behavior of Cement Grout in Presence of Superplasticizer

Effect of Bentonite on the Rheological Behavior of Cement Grout in Presence of Superplasticizer

Impact of delayed addition time of SNF condensate on the fire resistance and durability of SRC–SF composite cement pastes

This work aimed to investigate the impact of delayed addition time (DAT) of sulphonated naphthalene formaldehyde (SNF) superplasticizer on the durability and fire resistance of SRC–SF composite cement pastes immersed in both 4% MgCl2 or 4% MgSO4 solutions as well as at elevated temperatures up to 800°C, respectively. The results indicate that, the compressive strength and bulk density of cement paste increase with DAT at 7.5min up to 90days in tap water. The cement pastes admixed with 1.0mass% of SNF condensate at delayed addition time 7.5min, which cured in both 4% MgCl2 or 4% MgSO4 for 1year or thermally treated up to 800°C, has the highest durability and fire resistance. This is mainly due to that, the presence of superplasticizer with delayed addition process of mixing, reduces the water demand for standard consistency, decreases the total porosity, and increases the bulk density and consequently the compressive strength of cement pastes. These factors work together to modify the microstructure producing homogeneous compact closed structure. Total sulphate and chloride contents decrease with SNF content and DAT, due to decrease the accessibility of SO42- and Cl− to penetration into the pore system to form ettringite and chloroaluminate hydrate which expands and softens the cement paste matrix at later ages.