Influence of superplasticizers on the early-age crack resistance of concrete

In order to improve the early-age cracking resistance of concrete, different types of superplasticizers are used. Two types of polycarboxlic salt/acid superplasticizers and one retarding naphthalene superplasticizer are selected to investigate the influence of superplasticizers on the early-age cracking resistance of the concrete by using the slab test and the temperature-stress test. The results show that the polycarboxlic salt/acid superplasticizer cannot always improve the cracking resistance capacity of the concrete compared with the naphthalene superplasticizer, which is related to the chemical structure of the polycarboxlic salt/acid superplasticizer. High plastic tensile strength and dynamic elastic modulus at the early stage are beneficial to avoid cracking, and low hydration heat is also helpful. The evolutions of the drying shrilakage stress and the hydration heat temperature stress varying with time can be comprehensively evaluated by means of the slab test and the temperature stress test.

Effect of Crosslink Structure of Bridge Polycarboxylate Superplasticizers on Dispersion Ability

Bridge polycarboxylate superplasticizers（PCs） with crosslink structure were synthesized by using polyethyleneglycol di-acrylate（PEGdA）, replacing partial polyethyleneglycol mono-acrylate （PEGmA） as crosslinking agent. Structures of bridge PCs were analyzed by gel permeation chromatography, and dispersion ability was evaluated by cement paste dispersity variation on time and rheology test. The experimental results showed that, molecular weight（MW） of bridge PCs increased with increase of PEGdA proportion, and MW distribution curve changed from Gaussian to fiat like, which meant notable increase of highly crosslinked copolymer. Bridge PCs led to decreased initial cement paste dispersity and better dispersity retention due to slow releasing. Further research showed that, PEGdA proportion had slight effect on polymerization degree of backbone, MW distribution of backbone deviated from Gaussian distribution and shoulder peaks appeared on distribution curve when PEGdA increased.

The Compatibility of Polycarboxylate-Type Superplasticizers with Cement

Four polycarboxylate- type （ PC ） superplasticizers of different functional groups were used ; their dispersing and retaining behaviors were analyzed through ZETA potential measurement, mini-slump test of cement paste and performance test of concrete. The experimental results show that the dispersing and flow-retaining ability of PC was determined by two factors of anionic groups and nonionic groups ： the density of anionic groups - COO^- or - SO3^- acted on the electronic repulsive force. and the length and proportion of nonionic graft groups of PEO in PC chemical stracture affected the steric effect. The compatibility between PC superplasticizers and cement mainly depended on the type of PEO groups ; furtlwrmore, adding mineral powders is good to the compatibility for high performance concretes （ HPCs ）.

Influence of Superplasticizers on Strength and Shrinkage Cracking of Cement Mortar under Drying Conditions

The effects of polynaphthalene series superplasticizers（PNS） with a low content of sodium sulfate （H-UNF）,with a high content of sodium sulfate（C-UNF） and polycarboxylate type superplasticizer （PC） on strength and shrinkage cracking of cement mortar under drying conditions were 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 the initial cracking time of mortars, and decrease the cracking sensitivity of mortars. As for decreasing the cracking sensitivity of mortars, PC〉H-UNF〉C-UNF. To incorporate superplasticizers is apparently to increase the free shrinkage of mortars when keeping the constant w/b ratio and the content of cement pastes. As for the effect of controlling the volume stability of mortars, PC〉C-UNF〉H-UNF. Maximum crack width of mortars containing PC is lower, but the development rate of maximum crack width of mortars containing H-UNF is faster in comparison with control mortars. The flexural and compressive strengths of mortars at 28-day increase with increasing superplasticizer dosages under drying conditions. PC was superior to PNS in the aspect of increasing strength.

Effect of molecular structure and slump loss resistance of polycarboxylate superplasticizers on self-compacting concrete

A new kind of polycarboxylate superplasticizer with high slump loss resistance was obtained by designing scheduled molecular structure.The number average molecular mass of the polymer was characterized by the gel permeation chromatography measurements.And chemical structure of the polymer was observed by the Fourier transform infrared spectroscopy(FT-IR).The results show that the good workable maintaining of self-compacting concrete could be achieved through direct adjustment of number average molecular mass and different unsaturated monomer in synthetic process.The FT-IR analysis illustrated that the high slump loss resistance of polycarboxylate superplasticizers with ester and carboxyl group and expectations of molecular structure were designed.

Coupled effect of viscosity enhancing admixtures and superplasticizers on rheological behavior of cement paste

The coupled effect of viscosity enhancing admixtures(VEA)and superplasticizer(SP)on the rheological behavior of cement paste was investigated in this work.Two types of VEAs,including hydroxypropyl methylcellulose(HPMC)and Welan gum,and two types of SPs,i.e.polycarboxylate(PCA)and polynaphthalenesulfonate(PNS)were used as admixtures for cement paste.Rheological curves of cement paste and simulated pore solution containing VEA and SP were tested.Simulated pore solution test results show that molecules of different SPs may generate different effects on the viscosity of VEA solutions.Hershel-Bulkley(H-B)model was used to fit rheological curve of cement paste.Strong interaction between PNS and HPMC was observed in this work.

Adsorption of Superplasticizers in Fly Ash Blended Cement Pastes and Its Rheological Effects

The adsorption of superplasticizers in fly ash blended cement paste and its rheological effects were investigated.It is shown that the absorption of superplasticizer on portland cement particles is very different from that on fly ash particles.The fly ash particles have smooth surfaces and are negatively charged,so its adsorption capacity is weaker than the portland cement particles.The amount of adsorbed SP in the fly ash blended cement paste depends highly on the replacement proportion of portland cement with fly ash,and to a much less extent on the nature of the fly ash.However,the amount of adsorbed superplasticizer does not correspond well the ζ-potential of the solid particles,due the strong adsorbing capacities of the Portland cement particles.When fly ash replaces portland cement in the paste,the rheological behavior is radically changed,which is closely related to the fineness and density of the ash.The packing and agglomeration of the solid particles are the controlling factors on the rheological parameters of the fresh paste,instead of the amount and type of adsorbed superplasticizer.

Influence of Superplasticizers on Early Age Drying Shrinkage of Cement Paste with the Same Consistency

The influence of superplasticizer（SP） on the early age drying shrinkage of cement paste with the same consistency was investigated. To conduct the test, which lasted for 72 hours, three paste mixtures were used for comparison. The 72 hours early age drying shrinkage staring from the initial setting time was measured by a clock gauge. The pore size distribution was measured by Mercury Intrusion Method. The surface tension of capillary simulation liquid and mass loss of paste were also measured. The experimental results showed that the addition of SP increased the early drying shrinkage greatly. The ratios of water evaporation and the total free water in mixtures added with SPs showed great differences. SPs fined the capillary pores of paste, and the volume of pore with diameter within 50 nm was well consistent with shrinkage rate. The addition of SPs did not raise the capillary liquid surface tension. It showed that with the volume of pore with diameter within 50 nm and the ratio of water evaporation and the total free water a tolerable shrinkage result of paste added with SP could be predicted, and the elastic modulus could have an influence on the early shrinkage. These results have never been proposed before.

Effect of Superplasticizers on the Early Age Hydration of Sulfoaluminate Cement

The effects of two types of superplasticizers on the properties of CSA cement pastes during early hydration were studied. The influences of two types of superplasticizers on the properties of cement pastes, including the normal consistency, setting time, fl uidity, and compressive strength, were investigated by using various methods. The hydration products of the cement pastes cured for 1 day and 3 days were studied by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results show that the PCE type superplasticizer retards the early age hydration while the FDN type superplasticizer accelerates the early age hydration of the CSA cement. Both types of superplasticizers have no infl uence on the further hydration of CSA cement, confi rmed by the calorimeter tests as well. The ultrasonic pulse velocity measurements were used to probe the influence of two types of superplasticizers on the hydration of CSA cement pastes at a high water-cement ratio（0.45）. The results show that the PCE type superplasticizer retards the early age hydration of the CSA cement while the FDN type superplasticizer has little infl uence on the early age hydration of the CSA cement.

Chemical Structures and Adsorptive Behaviors of Superplasticizers on β-C_2S

The chemical structures of four types of superplasticizers （SPs） and their adsorptive behaviors on β-C2S were investigated. The adsorption properties of SPs on β-C2S were measured and the relationship between the adsorption quantity and the specific surface of β-C2S was analyzed. The experimental results show that the adsorption quantity increases with the surface area increase of β-C2S, but the adsorption quantity per surface area is similar, which means that the main adsorbent is β-C2S itself. Polycarboxylic ester （PCE） showed the highest adsorption amount on β-C2S, followed by β-naphthalene sulfonates （NSF） and formaldehyde-acetone condensates sulfonates （FAS）, amino sulphonate （AS） showed the least adsorption amount on β-C2S. PCE affected the surface potential of β-C2S particles in water differently in comparison with other types of SPs. The adsorption capacity of SPs on β-C2S is determined by factors such as molecular structure, functional groups and molecular weight of SPs.

Influences of Polycarboxylate Superplasticizers on Rheological Behavior of Low-cement Castables

Influences of different superplasticizers （ STP. KSJSTO and LMS-P） on rheological behavior of low-cement castables and the mechanisms were analyzed. The shear stress and viscosity under different shear rates of matrix slurry were determined using a NXS-I IA rotary viscometer. Effects of different admixtures on the rheological properties of slurry was analyzed theoretically. Sodium tripolyphosphate and poly＇carboxylate superplasticizers KS-JSTO and LMS-P） can improve the fluidity and initial setting time. With STP. the slurry is plastic flow. With KS-JS70 or LMS-P increasing, the slurrv changes from plastic.flow, pseudoplastic flow to dilatant flow successively. Th, e optimum dosages of STP. KS-JSTO and LMS-P are 0. 15%. 0. 25% and 0. 40%, respectively. KS-JS70 and LMS-P can significantly reduce the slurry viscosity and shear stress to improve the workability of construction. Both shear stress and viscosity shall be taken into account for on-site construction.

Rheological Properties of Recycled Aggregate Concrete Using Superplasticizers

The mechanical properties of recycled aggregates concrete from demolition have been studied for several years. It has been documented that rheological properties of these concrete are generally affected by use of recycled aggregates. They could present mechanical properties less affected by the presence of recycled aggregates if the initial concrete were of good quality. However, manufacturing problems, mainly attributed to the angular character of these aggregates and to the granulometry of recycled sand, limit their industrial use. The worth point of this study consists in the optimization of the concrete formulation using specific admixture, adapted to this aggregates in order to facilitate its manufacturing. It shows that the new generation of superplasticizers containing some copolymer polycarboxylate makes it possible to significantly improve the fluidity of the recycled aggregates concrete in its fresh state. The aim of this research is to control rheologica] properties of fresh recycled aggregates concrete with fine and coarse recycled aggregates to limit the negative influence of aggregates on mechanical properties of concrete.

Influences of Soluble Salts on Adsorption Properties of Polycarboxylate Superplasticizers

Polycarboxylate（PC） superplasticizers with different chemical structures were synthesized through free radical co-polymerization reaction.A total organic carbon analyzer was used to investigate adsorption behaviors of PCs,and to evaluate influences of soluble salts on absorption properties of PCs.It is found that adsorption ratios of PCs on cement particles decrease greatly with the addition of Na2SO4;the adsorption ratio of ethers PC with Hydroxyethyl methacrylate（HEMA） group first increases then decreases with the addition of NaCl;the adsorption ratio of esters PC with short side chains first decreases then increases,while the adsorption ratio of ethers PC with HEMA group decreases with the addition of CaCl2;the adsorption ratio of esters PC with short side chains decreases with the addition of Ca（NO3）2;AlCl3 causes the decrease of the adsorption ratio of ethers PC with HEMA group.

The Effect of Various Polynaphthalene Sulfonate Based Superplasticizers on the Workability of Reactive Powder Concrete

A superplasticizer is a type of chemical admixture used to alter the workability(viscosity)of fresh concrete.The workability of fresh concrete is often of particular importance when the water-to-cement(w/c)ratio is low and a particular workability is desired.Reactive Powder Concrete(RPC)is a high-strength concrete formulated to provide compressive strengths exceeding 130MPa and made of primarily powders.RPC materials typically have a very low w/c,which requires the use of a chemical admixture in order to create a material that is easier to place,handle and consolidate.Superplasticizer are commonly used for this purpose.Superplasticizers are developed from different formulations,the most common being Polycarboxylate Ether(PCE),Polymelamine Sulfonate(PMS),and Polynaphthalene Sulfonate(PNS).This study investigates the effect of various PNS based superplasticizers on the rheological performance and mechanical(compressive strength)performance of a RPC mixture.Six distinctive types of PNS based superplasticizers were used;three of various compositional strengths(high,medium,low range)from a local provider,and three of the same compositional strengths(high,medium,low)from a leading manufacturer.The properties investigated were the individual superplasticizers’viscosity,the concrete workability,determined through a mortar spread test,the concrete viscosity,and the compressive strength of the hardened RPC mixtures measured at 7,14,and 28 days.Two separate RPC mixtures were prepared,which contained two different water-to-cementitious ratios,which consequently increases the dosage of superplasticizer needed,from 34.8L/m3 to 44.7L/m3.The results show that the name brand high range composition produced the overall highest spread,lowest viscosity,and a highest compressive performance.However,the local provider outperformed the name brand in the mid and low range compositions.Lastly,the rheology assessment also confirmed that the name brand high range,and RPC fabricated with the name brand high range,developed the lowest viscosities.

Effect of recycled powder on the yield stress of cement paste with varied superplasticizers

The influence of superplasticizer on the yield stress of cement pastes with recycled powder(RP)was examined in the study.Four superplasticizers were used to obtain the similar fluidity by adjusting the dosage.The results show that the 10%RP decreases the yield stress of paste compared to the reference paste at the same fluidity,but 20%and 30%RP increases the yield stress,ranging from 11 to 599%.The superplasticizer with adsorptive group of phosphate-type minimizes the yield stress of paste than that of polycarboxylate-type,but it made a significant increment in yield stress as the incorporating of RP increased.Besides,the polycarboxylate superplasticizer with the higher molecular weight of side chain and charge density led to lower yield stress.Based on the Yodel model,the yield stress of paste with RP was analyzed by the polymer adsorption and particle packing density of particles to reveal the influence of RP with different superplasticizers on the colloidal interaction and contact network among the particles.The packing density of particles with recycled powder was a little higher than the reference paste,but the higher fraction of fine particles made a stronger PSD effect,which improved the particle contact interaction.On the other hand,due to the higher polymer adsorption of recycled powder than cement,especially for superplasticizer with phosphate group,the average surface coverage was increased,which extended the separation distance,so that colloidal interaction among particles was weaken.

Superplasticized vs. Conventional Concrete: A Comparative Review

The global awareness and utilization of superplasticizers (SPs) in concrete have significantly contributed to developing resilient and sustainable infrastructure. Despite this, many developing nations face limited adoption of SPs in construction practices due to a lack of knowledge. This study provides a concise overview of concrete’s mechanical and durability properties, comparing formulations with and without superplasticizers. The focus is on compressive and flexural strengths, modulus of elasticity, water sorptivity, and chloride penetration. The results underscore the considerable improvement in both mechanical and durability properties when SPs are incorporated. The study recommends the widespread use of SPs, particularly in developing countries, to enhance the longevity of concrete structures.

Microstructural evolution and deformation mechanisms of superplastic aluminium alloys:A review

Aluminium alloy is one of the earliest and most widely used superplastic materials.The objective of this work is to review the scientific advances in superplastic Al alloys.Particularly,the emphasis is placed on the microstructural evolution and deformation mechanisms of Al alloys during superplastic deformation.The evolution of grain structure,texture,secondary phase,and cavities during superplastic flow in typical superplastic Al alloys is discussed in detail.The quantitative evaluation of different deformation mechanisms based on the focus ion beam(FIB)-assisted surface study provides new insights into the superplasticity of Al alloys.The main features,such as grain boundary sliding,intragranular dislocation slip,and diffusion creep can be observed intuitively and analyzed quantitatively.This study provides some reference for the research of superplastic deformation mechanism and the development of superplastic Al alloys.

The Influence of Chemical Admixtures on the Fluidity,Viscosity and Rheological Properties of Ultra-High Performance Concrete

To achieve higher strength and better durability,ultra-high performance concrete(UHPC)typically employs a relatively small water-binder ratio.However,this generally leads to an undesired increase in the paste viscosity.In this study,the effects of liquid and powder polycarboxylate superplasticizers(PCE)on UHPC are compared and critically discussed.Moreover,the following influential factors are considered:air-entraining agents(AE),slump retaining agents(SA),and defoaming agents(DF)and the resulting flow characteristics,mechanical properties,and hydration properties are evaluated assuming UHPC containing 8‰powder PCE(PCE-based UHPC).It is found that the spread diameter of powder PCE is 5%higher than that of liquid PCE.Among the chemical admixtures studied,AEs have the best effect on improving UHPC workability,while DFs have the worst effect.When the addition of AE and SA is 1.25‰and 14.7%of PCE,paste viscosity reduces by 35%and 19%,respectively compared to the paste with only 8‰PCE.A low AE dosage(1.25‰)decreases compressive strength by 4.1%,while SA(8.1%)increases UHPC compressive strength by 9.1%.Both AE and SA significantly delay the UHPC hydration process,reducing the hydration heat release peaks by 76%and 27%,respectively.

Effects of Mineral Admixtures and Superplasticizers on Micro Hardness of Aggregate-Paste Interface in Cement Concrete

This paper presents quantitatively the results of an experimental investigation on influence of mineral admixtures and superplasticizers on Vickers micro hardness(HV) of aggregate-paste interface in cement concrete. The HV was measured by Vickers hardness testing equipment.The results indicate that addition of fly ash decreases HV of the concrete.Although it decreases with the increase of ground granulated blast furnace slag (GGBS) replacement,the HV is higher than that of concrete containing fly ash at all replacements.The flying ash and GGBS composition increases HV in later curing ages,but does not improve it in early curing ages.Aminosulfonic acid based superplasticizer and aliphatic hydroxy sulphonate condensate superplasticizer can enhance HV in early curing ages.The HV of concrete with polycarboxylic acid superplasticizer is higher in later curing ages.

Influence of High-Robustness Polycarboxylate Superplasticizer on the Performances of Concrete Incorporating Fly Ash and Manufactured Sand

Using ethylene glycol monovinyl polyoxyethylene ether,2-acrylamido-2-methylpropane sulfonic acid(AMPS)and acrylic acid as the main synthetic monomers,a high robustness polycarboxylate superplasticizer was prepared.The effects of initial temperature,ratio of acid to ether,amount of chain transfer agent,and synthesis process on the properties of the superplasticizer were studied.The molecular structure was characterized by GPC(Gel Permeation Chromatography)and IR(Infrared Spectrometer).As shown by the results,when the initial reaction temperature is 15℃,the ratio of acid to ether is 3.4:1 and the acrylic acid pre-neutralization is 15%,The AMPS substitution is 10%,the amount of chain transfer agent is 8%,and the performance of the synthesized superplasticizer is the best.Compared with commercially available ordinary polycarboxylate superplasticizer in C30 concrete prepared with manufactured sand and fly ash,the bleeding rate decreases by 52%,T50 decreases by 1.2 s,and the slump time decreases by 1.1 s.In C60 concrete prepared with fly ash and river sand,the bleeding rate decreases by 46%,T50 decreases by 0.8 s,and the slump time decreases by 3.2 s.