Fluidity Of Paste Research Articles

A study to improve the compatibility of PCE with cement paste containing clay

Due to the stronger adsorption of polycarboxylate ether (PCE) superplasticizers to clay than cement particles, PCE fails to adjust the workability of cement paste containing clay. In this study, hexadecyl trimethyl ammonium bromide (CTAB) was used as an efficient clay-specific sacrificial agent to make PCE more compatible in cement paste containing Montmorillonite (Mt, one kind of clay). The experimental results indicated that CTAB can obviously improve the fluidity of cement paste containing Mt, with the increasing of spread diameter in the mini slump test. CTAB as a macromolecular compound with positive charge was able to interact with Mt by electrostatic adsorption, which was effective to hinder the hydration and swelling of Mt and therefore broke the absorption of Mt to PCE. In conclusion, CTAB has great potential to resolve the incompatibility of PCE to cement paste containing clay and contributes to the corresponding enhanced workability.

Study on adsorption and rheological properties of polycarboxylate superplasticizer with different structures

The chemical structures of different types of polycarboxylate superplasticizers were characterized by gel chromatography. The results showed that except PCE-5 was short main chain and short branch chain, the other polycarboxylate superplasticizers were long side chain structures. The properties of the superplasticizer were evaluated by the pulp experiment, and the adsorption and action mechanism were analyzed by testing the adsorption capacity and rheological parameters. The results showed that the order of saturated adsorption capacity of polycarboxylate in cement was PCE-5 > PCE-4 > PCE-3 > PCE-1 > PCE-2. The fluidity of paste is proportional to the adsorption amount of water reducing agent in paste. The thixotropic retention capacity of paste increased with the increase of polycarboxylate adsorption capacity.

Investigation of the early-age performance and microstructure of nano-C–S–H blended cement-based materials

Abstract Nano calcium silicate hydrate (nano-C–S–H) has become a novel additive for advanced cement-based materials. In this paper, the effect of nano-C–S–H on the early-age performance of cement paste has been studied, and some micro-characterization methods were used to measure the microstructure of nano-C–S–H-modified cement-based material. The results showed that the initial fluidity of cement paste was improved after addition of nano-C–S–H, but the fluidity gradual loss increased with the dosage of nano-C–S–H. The autogenous shrinkage of cement paste can be reduced by up to 42% maximum at an appropriate addition of nano-C–S–H. The mechanical property of cement paste was enhanced noticeably after adding nano-C–S–H, namely, the compressive strengths were improved by 52% and 47.74% at age of 1 day and 7 days, respectively. More hydration products were observed and pore diameter of cement matrix was refined after adding nano-C–S–H, indicating that the early hydration process of cement was accelerated by nano-C–S–H. This was mainly attributed to seed effect of nano-C–S–H. The detailed relationship between microstructure and early-age performance was also discussed.

Using the negative hydration of inorganic salt ions to improve the properties of Alkali-activated slag cement in plastic stage

Alkali-activated slag (AAS) cement is a low-carbon environmentally friendly cementitious material. Water glass (WG) activated slag cement has excellent physical and mechanical properties, but it is not conducive to the construction due to its rapid setting and hardening, easy loss of fluidity. Negative hydration ions can reduce the viscosity of aqueous solution. So, in the present paper, inorganic salt composed of negative hydration ions were used to adjust the fluidity and setting time of AAS paste. The results show that with the increase of NaCl, KCl, KBr and KNO3, the initial fluidity of AAS paste increases slightly, and the 30 min fluidity increases a lot, while the fluidity at 60 min is greatly affected by the amount of inorganic salt. KNO3 shows the greatest initial fluidity increase. When 0.2% Ba(NO3)2 is added with other four inorganic salts, the fluidity retention is significantly improved, especially the fluidity of 60 min. When 5% NaCl, KCl, KBr and KNO3 respectively mixed with 0.2% Ba(NO3)2 are added, the fluidity retention of AAS paste at 60 min are 97.4%, 92.7%, 100%, 82.5% respectively. Compared with the AAS paste without inorganic salt, when 5% NaCl, KCl, KBr and KNO3 respectively blended with 0.2% Ba(NO3)2 are added, the initial setting time increase by 228.6%, 285.7% 307.1% and 239.3%, while the final setting time increase by 175.6%, 222.0%, 231.7% and 178.0% respectively. With the inorganic salt, the ζ-potential of the originally negative AAS cement suspension become more negative, both yield stress and plastic viscosity coefficient decease, especially the plastic viscosity coefficient greatly reduces. This may be the reason for the change of fluidity and setting time of AAS paste.

Osteogenic potential and properties of injectable silk fibroin/tetracalcium phosphate/monetite composite powder biocement systems.

The powdered cement tetracalcium phosphate/monetite/silk fibroin composite (CFIB) was prepared by simple mechanical milling of tetracalcium phosphate/monetite powder mixture with fibrous soluble silk fibroin (SF). The powder composite cement mixtures contained 5 and 10wt % of SF and 2% NaH2 PO4 solution with 0.1% genipin was used as a liquid component. The setting time of CFIB cement increased with addition of SF from 5 to 25 min in fully injectable cement with 10wt % of SF. The compressive strength of hardened composites was reduced to 14 MPa which is close to strength of cancellous bone. The 8% of SF from origin amount in CFIB composites was only desorbed from cements after 7 days soaking in simulated body fluid (SBF). It was found almost full transformation of calcium phosphate components in composite to rod-like nanohydroxyapatite after hardening of CFIB cements in SBF. The SF in hardened cements was present in fine globular form after dissolution, actively affected the fluidity of pastes, morphology of hydroxyapatite particles, and microstructure. The excellent cell proliferation and a high over expression of osteogenic gene markers in MSCs were confirmed after the long-time cultivation in CFIB10 cement extract. Injectable CFIB10 cements have appropriate properties for utilization in bone defect treatments with possible positive effect on healing process.

Effect of Waste Ceramic Powder on Properties of Alkali-Activated Blast Furnace Slag Paste and Mortar.

Every year, ceramic tile factories and the iron smelting industry produce huge amounts of waste ceramic tiles and blast furnace slag (BFS), respectively. In the field of construction materials, this waste can be used as a raw material for binders, thus reducing landfill waste and mitigating environmental pollution. The purpose of this study was to mix waste ceramic powder (WCP) into BFS paste and mortar activated by sodium silicate and sodium hydroxide to study its effect on performance. BFS was partially replaced by WCP at the rate of 10–30% by weight. Some experimental studies were conducted on, for example, the fluidity, heat of hydration, compressive strength testing, ultrasonic pulse velocity (UPV), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electrical resistivity, sulfuric acid attack, and chloride ion diffusion coefficient. Based on the results of these experiments, the conclusions are: (1) increasing the amount of waste ceramic powder in the mixture can improve the fluidity of the alkali-activated paste; (2) adding waste ceramic powder to the alkali-activated mortar can improve the resistance of the mortar to sulfuric acid; (3) adding waste ceramic powder to the alkali-activated mortar can increase the diffusion coefficient of chloride ions; (4) the early strength of alkali-activated mortar is affected by the Ca/Si ratio, while the later strength is affected by the change in the Si/Al ratio.

Study on the Effects of Ultrasonic Agitation on CO2 Adsorption Efficiency Improvement of Cement Paste

To realize high-efficiency CO2 absorption by fresh cement paste, ultrasonic vibration technology is introduced into the CO2 absorption test device used in this study. Influences of ultrasonic frequency on the CO2 absorption rate (CO2 AR) and the ultimate absorption amount of fresh cement paste are analyzed. Furthermore, the influencing laws of the CO2 absorption amount (CO2 AA) on the fluidity, pore distribution, and mechanical properties of cement paste under ultrasonic vibrating agitation are analyzed by measuring the variations of the CO2 AA of cement paste. Results demonstrate that ultrasonic vibrating agitation not only can increase the CO2 AR and ultimate absorption amount of fresh cement paste, but also can optimize the internal pore structure of materials and compressive strength of cement-based materials.

Enhancing the application of mechanochemistry in the synthesis of high-concentration polycarboxylate superplasticizer: is aqueous copolymerization needed?

Mechanochemical synthesis, a rapid and efficient method, was utilized in the synthesis of polycarboxylate superplasticizers (PCEs) for the first time. For comparison, traditional polycarboxylate superplasticizer (TPCE) was also synthesized by the aqueous solution copolymerization method. The molecular structure of PCEs synthesized by mechanochemistry (MPCEs) and TPCE were confirmed by gel permeation chromatography, Fourier transform infrared spectroscopy, and 1H-nuclear magnetic resonance spectroscopy. The molecular weight of the synthesized MPCEs decreases with increasing reaction time in mechanochemical synthesis. Additionally, the concentrations of MPCEs and TPCE and the fluidity of the cement paste with MPCEs and TPCE were also investigated. MPCEs were found to have a much higher concentration than TPCE. When PCEs are added at 0.30 wt% of the cement dosage, the fluidities of the cement slurry with MPCE-A3 or MPCE-B3 are comparable to those of TPCE.

Effect of Nano-Magnesium Oxide on the Expansion Performance and Hydration Process of Cement-Based Materials.

Many scholars are concerned about the effect of nano-MgO as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties. This article examines the influence of nano-MgO on the long-term consistency, fluidity, expansion stability, hydration, and mechanical properties of 30% fly ash cement-based materials and improves research into nano-MgO as an expansion agent. Expansion performance, flexural and compressive strength, and stability after boiling and autoclave treatment were tested for specimens mixed with a 2, 4, 6, 8 and 10% cementitious material mass of nano-MgO. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were employed to study their hydration process and microstructure. The results showed that nano-MgO had an obvious effect on the consistency, fluidity and expansion performance of cement paste. After curing in water for 365 days and autoclaving thereafter, the hydration of nano-MgO was relatively complete. The volumetric expansion pressure of the magnesium hydroxide (Mg(OH)2) crystals and the crystallization pressure generated after their continuous precipitation were the main reasons for the expansion of the slurry. Nano-MgO improved the microstructure of cement paste and significantly enhanced its long-term flexural strength and compressive strength. When the content of nano-MgO was less than 10%, the cement with 30% fly ash had good long-term stability with the potential to compensate for the shrinkage of large-volume concrete.

Early hydration behavior of novel amphoteric polymer in cement paste

The development of the early strength of the concrete mainly depends on the early hydration process of the cement, and there are many factors influencing the early hydration process of the cement. It is of great significance to study the mechanism of the polymer on the cement hydration for the development of the product. The amphoteric polymer was synthesized by (2-propenyloxyethyl) trimethyl ammonium chloride, acrylic acid and isopentene polyoxyethylene ether with different molar ratio. The chemical structure of polymer was characterized by GPC, and the performance of cement with polymers was observed by isothermal calorimetry and compressive strength of mortar. The results showed that the new amphoteric polymer has a strong promoting effect on the early hydration of cement. With the increase of the amount of (2-propenyloxyethyl) trimethyl ammonium chloride, the hydration speed is faster, but the addition of amphoteric polymer results in the decrease of fluidity of cement paste, so it is necessary to control its amount reasonably.

Early‐age behavior and mechanical properties of cement‐based materials with various types and fineness of recycled powder

AbstractRecycled powder (RP) that includes recycled paste powder (RPP), recycled mortar powder (RMP), and recycled concrete powder (RCP) is an eco‐friendly alternative binder. This work investigated the influence of RP types and fineness on early‐age behavior and mechanical strength of cement‐based materials. The results show that substituting RP for cement causes the reduction of new hydration products in cement‐based materials. The blended RP decreases the fluidity of paste mixture, and the fluidity of paste including fine RPP is lower than that of paste including fine RMP and RCP; moreover, the fluidity increases following the growth of RP particle size. Incorporating fine RPP shortens the setting time of cement‐based materials, while the setting time is prolonged as RMP and RCP incorporate; in addition, the enlarged particle size of RP prolongs the setting time. The drying shrinkage increases following the increasing replacement ratio of RPP. Incorporating less proportion of fine RMP and RCP lessens the drying shrinkage of paste, while the drying shrinkage increases after coarse or high‐volume RMP and RCP substituting. The maximum shrinkage of paste including 30% fine and coarse RCP is 3.4% and 7.3% higher than that of plain paste. Substituting fine RP for less dosage of cement has less impact on the mechanical strength of its newmade mortar, while the mechanical strength markedly decreases after high‐volume or coarse RP substituting. The compression strength of mortar including 30% fine and coarse RCP is 22.2% and 35.1% lower than that of plain mortar.

Influence of Glass Powder on Rheological Properties of Ultra-High Performance Concrete Paste

Replacing cement and silica fume with glass powder to prepare ultra-high performance concrete (UHPC) is beneficial to solve the ecological problem in the field of civil engineering, but the technologies of preparation, transportation, pumping, and hardening of UHPC mainly relate to its rheological property. Therefore, this paper studied the influence of glass powder on the rheological properties of UHPC paste by performing the flow and the rheological test. Experimental results showed that when the cement and silica fume partially replaced by glass powder, the UHPC paste appears shear thickening, yield stress, plastic viscosity, and area of hysteresis loop decrease. This means that mixing glass powder can somehow inhibit the problems of segregation and bleeding of UHPC during pumping. In this manner, the dosage of the superplasticizer in UHPC is appropriately reduced, the filling capacity of UHPC during pouring is improved, and the energy required for UHPC in the pumping process is weakened. Compared with replacing cement, replacing silica fume with glass powder significantly increases the shear thickening and fluidity of UHPC paste, and at the same, reduces its yield stress and plastic viscosity. This indicates that the construction performance of UHPC is greatly improved with the replacement of silica fume. The fluidity and yield stress of UHPC paste satisfy the quadratic polynomial function relationship, and the replacement of cement and silica fume with glass powder should be less than 33% and 50%, respectively. Under this condition, the rheological properties of the UHPC paste are greatly improved and result in little negative impact on the mechanical properties of UHPC.

The Influence of Water Reducing Agents on Early Hydration Property of Ferrite Aluminate Cement Paste

The ferrite aluminate cement (FAC) could rapidly lose fluidity or workability due to its excessive hydration rate, and greatly reduce the construction performance. Chemical admixtures are commonly used to provide the workability of cement-based materials. In this study, to ensure required fluidity of FAC, chemically different water reducing agents are incorporated into the FAC pastes. The experiments are performed with aliphatic water reducing agent (AP), polycarboxylic acid water reducing agent (PC) and melamine water reducing agent (MA), respectively. Influence of the water reducing agents on fluidity, setting time, hydration process, hydration product and zeta potential of the fresh cement pastes is investigated. The results show that PC has a better dispersion capacity compared to AP and MA. Besides decreasing water dosage, PC also acts as a retarder, significantly increasing the setting times, delaying the hydration rate and leading to less ettringite in the hydration process of FAC particles. The water reducing agents molecules are adsorbed on the surface of positively charged minerals and hydration products, however, for PC, steric hindrance from the long side chain of PC plays a critical role in dispersing cement particles, whereas AP and MA acting through an electrostatic repulsion force.

Influence of Lightly Burned MgO on the Mechanical Properties and Anticarbonization of Cement-Based Materials

This study aims to study the influence of a lightly burned magnesium oxide (LBMO) expansion agent on the rheological properties (the slump flow, plastic viscosity and variation of shear stress) of cement-based materials. Four different mass contents (i.e., 0%, 3%, 6% and 9%) of LBMO were selected. The following compressive strength and expansion value of the corresponding cement concrete were tested. Cement concrete with two strength grades of 30 MPa and 50 MPa (C30 and C50) was selected. Results indicated that the addition of LBMO can effectively decrease the fluidity and increase the plastic viscosity of fresh cement paste. An optimum dosage (3%) of LBMO is the most advantageous to the compressive strength of cement concrete. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. Moreover, the incorporation of LBMO led to a reduction in the fluidity of the cement paste and an increase in plastic viscosity. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. It can be found that little difference exists in the compressive strength and the expansion rate of cement concrete with strength grades of 30 MPa and 50 MPa. Finally, the increased dosage of LBMO, curing age and compressive strength led to improving the carbonization resistance of cement concrete.

Rheology and alkali-silica reaction of alkali-activated slag mortars modified by fly ash microsphere: a comparative analysis to OPC mortars

The poor workability and the risk of alkali-silica reaction (ASR) caused by alkaline activators restrict the wide range of applications of alkali-activated slag (AAS) cement. This paper presents a study on the effect of fly ash microsphere (FAM) on mitigating the rheological properties and ASR of AAS mortars for the first time. For comparison, the ordinary Portland cement (OPC) mortars blended with FAM are also prepared and investigated. The FAM addition is effective in decreasing the viscosity and meanwhile increasing the fluidity of the AAS pastes and mortars due to its ‘ball-bearings’ effect. According to the results obtained from the accelerated mortar bar test, the addition of more than 10% FAM reduces the ASR expansion effectively in both of the AAS and OPC mortars. Mineralogical studies demonstrate that for the AAS mortars, FAM promotes the formation of C-A-S-H gel phases with a better alkali binding capacity to mitigate ASR. The pozzolanic reaction of FAM consumes Ca(OH)2 in the OPC mortars, which is essential to the ASR development. In addition, minor ASR products are observed in the AAS or OPC mortars modified with FAM, and meanwhile there is a more strong bonding between the interface of aggregate-paste.

Working Mechanisms and Design Principles of Comb-like Polycarboxylate Ether Superplasticizers in Cement Hydration: Quantitative Insights for a Series of Well-Defined Copolymers

Cement and concrete are the most widely used building materials and contain comb copolymers such as polycarboxylate ethers (PCEs) as hydration and setting modifiers. The working mechanisms of these additives in cement hydration have remained uncertain, which limits the rational design of additives and of new cement materials with lower CO2 footprint. We identified quantitative correlations between PCE copolymer structure, adsorption, and cement setting properties for a series of copolymer structures and concentrations, combined with insights into conformations and adsorption mechanisms by atomistic simulations. The PCE copolymers have only a small fraction of polydispersity compared to earlier studies, and molecular dynamics simulations utilize Interface force field models for C-S-H phases that enable order-of-magnitude more accurate insights into the dynamics of the nanoscale polymer interfaces compared to earlier models. Two distinct sets of property correlations were discovered. (1) The carboxylate content of the PCEs, i.e., the molar density of ionic side groups per unit mass, correlates with the adsorbed amount of polycarboxylate ethers onto cement pastes, the conductivity of the cement paste, and the retardation of the acceleration period of cement hydration. (2) The combination of the ionic character of the polymer backbone and the length of non-ionic polyethylene glycol (PEG) side chains correlates with the water-to-cement ratio necessary for processing, zeta potentials, and fluidity of the cement pastes in mini slump tests. Simulations indicate that PCE adsorption onto cement particles involves migration of calcium ions in the acrylate backbone onto the calcium silicate hydrate surface, or calcium hydroxide surfaces, followed by ion pairing of the anionic polymer backbone with the positively charged mineral surface. PEG side chains exhibit no affinity to the mineral surface. The best fluidity and water reduction are achieved using an optimum ratio of the volume of PEG side chains to the volume of the anionic backbone, balancing sufficient surface bonding through the ionic backbone and minimization of interparticle forces by the non-ionic PEG side chains. A charge density too low prevents effective adsorption, and a charge density too high leads to multilayer deposition and ionic agglomeration forces between coated particles that reduce the fluidity and increase the necessary water-to-cement ratio. The proposed mechanism supersedes prior models and provides quantitative metrics for the rational design of polymer additives for cement and related particle dispersions.

Effect of Rheology of Fresh Paste on the Pore Structure and Properties of Pervious Concrete Based on the High Fluidity Alkali-Activated Slag

Pervious concrete is made of cementitious materials, coarse aggregate, water and additives, with characteristic macro- and meso-connected pore structure, which enables the acceptable mechanical properties and high water permeability for pavement and road applications. In this study, the effect of rheology of fresh alkali-activated slag paste on the sedimentation of paste on the bottom of pervious concrete, meso-structure, connected porosity, mechanical properties and water permeability was investigated by a range of analytical techniques through varying the equivalent alkali content to control the rheology of fresh paste in the pervious concrete. The compressive strength of pervious concrete was related to the percentage area of paste and the average thickness of paste on the surface of coarse aggregate. The tensile strength and water permeability were correlated to the connected porosity of pervious concrete and the rheology of fresh paste. A relative lower fluidity, higher viscosity and shear stress of fresh alkali-activated slag paste favoured lower sedimentation of paste on the bottom of pervious concrete, higher connected porosity, tensile strength and water permeability. There was no correlation between compressive strength and tensile strength of pervious concrete.

Effects of the combined usage of nanomaterials and steel fibres on the workability, compressive strength, and microstructure of ultra-high performance concrete

Abstract Using nanomaterials to enhance concrete performance is of particular interest to meet the safety and functionality requirements of engineering structures. However, there are few comprehensive comparisons of the effects of different nanomaterials on the properties of ultra-high performance concretes (UHPCs) with a compressive strength of more than 150 MPa. The aim of the present study was to assess the coupling effects of nanomaterials and steel fibres on the workability and compressive performance of UHPC. Three types of nanomaterials, nano-SiO2 (NS), nano-calcium carbonate (NC), and carbon nanofibre (CNF), were each added into UHPC mixes by quantity substitution of the binder; two types of steel fibres were investigated; and two mixing methods were used for casting the UHPC. In addition, the effect of curing age (7 or 28 days) on the compressive performance of the mixtures was considered. Comprehensive studies were conducted on the effects of these test variables on the fluidity, compressive strength, failure mode, and microstructure. The results show that the combination of these nanomaterials and steel fibres can provide good synergetic effects on the compressive performance of UHPC and that the addition of CNF results in a greater enhancement than the addition of NS or NC. The addition of NS, not CNF or NC, has a considerable negative influence on the fluidity of the UHPC paste. It is suggested that reducing the agglomeration of the nanomaterials would further improve the performance of the resulting UHPC.

Impact of Sulphate Ions Content on Performance of Maleic and Acrylic Superplasticizers in Cement Paste.

The paper presents test results of the impact of sulphate ions from calcium sulphates: Hemihydrate, dihydrate and anhydrite, on rheological properties and hydration heat of cement pastes with, and without, superplasticizers, derivatives of maleic (SP-2) and acrylic (SP-1) acids. It is demonstrated that cement pastes fluidity depends on superplasticizer chemical structure, and its effect is expressed by a hydrophilic coefficient. As maleic superplasticizers have flexible comb-like structure composed of a shorter backbone chain containing COO− carboxylate groups and very long side chains, cement pastes showed higher fluidity than with acrylic superplasticizer with ladder-like structure, longer backbone chains with shorter side chains. SP-1 showing lower hydrophilicity coefficient and fewer COO− groups was found to be less sensitive to increased sulphate ion content in pastes. However, with SP-2 with higher hydrophilicity, a gradual fluidity loss (increased paste viscosity) was observed. Plastic viscosity was approximately at the same level in SP-1-containing pastes. Tests showed that sulphates definitely changed polycarboxylate superplasticizers performance. A high concentration of sulphate ions reduced maleic superplasticizer efficiency. Under these conditions, SP-1 is more effective and therefore more suitable for fluidity of pastes containing higher SO42− ions content. Thus, sulphate ions concentration in the paste should be considered when selecting superplasticizer.

Technical optimization and life cycle assessment of environment-friendly superplasticizer for concrete engineering

With the rapid development of the construction industry, it is necessary to synthesize environment-friendly functional polymers, especially when developing “green” construction industry types. Herein a novel solid-state polycarboxylate superplasticizer (PCE) with low energy-consumption was designed and synthesized. In industrial application, solid-state PCE has exhibited better cement paste fluidity and concrete slump compared to liquid-state PCE. A life cycle assessment (LCA) of the PCE synthesis, the packaging materials used, and the transportation of the PCE were conducted based on the ReCiPe method. The results indicated that liquid-state PCE has a far greater environmental impact at >60% than solid-state PCE, which is less significant at <40%. The inventory data that are associated with the production of the new polymer are disclosed for the first time to enrich the related database in this field. This study demonstrates the optimization of the state and synthesis technique of a functional polymer, improving the performance and lowering the environmental impacts involved in producing the polymer, while reducing the risks to human health and protecting the ecosystem at the same time.