Polycarboxylate-based Superplasticizer Research Articles

Effect of mechanochemistry on graphene dispersion and its application in improving the mechanical properties of engineered cementitious composites

To improve the dispersibility of graphene in cement-based materials and achieve better mechanical properties, this study proposes a novel and practical mechanochemical grafting strategy through ball milling technique. The polycarboxylate-based superplasticizer was successfully grafted on graphene, inducing both covalent and non-covalent modifications of the graphene surface simultaneously. The mechanochemistry method under different conditions, e.g., dry milling or wet milling, was investigated. The dispersion efficiency of prefabricated graphene was compared with traditional ultrasonic dispersion methods. The graphene prepared with these dispersion methods was then applied to prepare Engineered Cementitious Composites (ECC). The results indicated that the proposed mechanochemical methods can effectively reduce particle size, increase specific surface area, and introduce abundant functional groups, thereby improving the dispersibility of graphene. Especially under wet milling conditions, smaller and more dispersed particles could be produced. The addition of well dispersed graphene at 0.1 wt% in engineered cementitious composites (ECC) showed a 24.0 % increase in compressive strength, a 32.4 % increase in tensile strength, and a 66.9 % increase in ultimate tensile strain. This improvement is attributed to the a capability of graphene sheets processed by ball milling to impede the propagation of cracks within the cement matrix.

Assessing hydration kinetics and rheological properties of Limestone Calcined Clay Cement (LC3): Influence of clay-mitigating and superplasticizer admixtures

Limestone calcined clay cements (LC3) signify a trend in the construction sector aimed at reducing environmental impacts. However, the fresh state behavior of these cements, especially concerning clay properties and their interaction with chemical admixtures, needs to be better understood and investigated. This study is designed to assess the impact of a polycarboxylate-based superplasticizer (ADV) and a clay-mitigating (CM) admixture, along with exploring the synergistic effects that arise from combining both admixtures on the properties of LC3 cements. Hydration kinetics were evaluated in cement pastes using isothermal calorimetry and in-situ XRD, while fresh state properties were evaluated by rotational rheometry. The calorimetry results showed that the CM admixture provides a delay in the aluminate reactions of all LC3 systems, while it does not significantly affect the hydration of Portland cement pastes, suggesting a pronounced interaction of this admixture with clay particles. The incorporation of the CM admixture did not yield favorable workability conditions in LC3 mixtures when compared to the effectiveness of the ADV. In general, the assessment indicates that the CM admixture lacks effective dispersion capabilities and exhibits a limited influence on the formation of hydrated products in LC3 cements produced with calcined kaolinitic clay.

Mathematical models of apparent viscosity as a function of water–cement/binder ratio and superplasticizer in cement pastes

The water–cement/binder ratio and the admixture of water-reducing agents strongly affect the rheological properties of cement pastes. This study develops mathematical models to predict the apparent viscosity of cement pastes with varying water-cement/binder ratios and polycarboxylate-based superplasticizer content by introducing the power law shear stress-shear strain relation of non-Newtonian fluids into the Navier–Stokes motion equations. The developed models are compared with the results of rheological experiments and verified for their accuracy in simulating the apparent viscosity of cement pastes. These models provide insight into the rheological behaviour of cement pastes and could have practical applications in the construction industry.

Effect of the molecular weight of sacrificial agents on superplasticizer interaction with clays on cement-based materials

The high affinity among polycarboxylate-based superplasticizer admixtures (PCEs) and aggregates containing trace amounts of clay has been considered one of the challenges in concrete production in recent years because of its impact on water and chemical admixtures demand as well as its effects on concrete performance. Two types of clays were identified as impurities in a natural sand deposit; therefore, two pure clays were selected, kaolinite (KGa-2) and illite–smectite (ISCz-1), with a cation exchange capacity (CEC) of 2.75 meq/100 g and 27.50 meq/100 g, respectively. As the main results, the adsorption isotherms with PCE using total organic carbon (TOC) showed 99 % adsorption of the admixture on ISCz-1 clay, increasing the interplanar distance from 10.68 Å to 11.54 Å, and decreasing the specific surface area, suggesting intercalation and physical adsorption between the admixture and the clay. For KGa-2 clay, PCE adsorption was about 79 %, with no measured changes in interplanar d-spacing and the specific surface area decreased slightly due to the kaolinite stability.A mitigation strategy based on two quaternary ammonium compounds as sacrificial agents with different molecular weights was tested: hexadecyltrimethylammonium bromide (HTB) and tetraethylammonium bromide (TTB), and their proportions were varied based on multiple of the cation exchange capacity of the clay (0.5,1.0,1.5,2.0,2.5 and 3.0 CEC). Surface changes on functionalized ISCz-1 showed a 76 % reduction in surface area for 1.0 CEC HTB and 21 % for 1.5 CEC TTB. Both molecules exhibited an increase in d-spacing, but in different patterns due to molecular weight and molecule structure. The results of mini-slump tests and rheological measurements indicate that a synergistic effect occurs with the PCE at higher molecular weight (HTB), which increases the flowability of the mortar and causes a decrease in yield stress.

Influence of polycarboxylate superplasticizer and calcium sulfoaluminate cement on the rheology, hydration kinetics, and porosity of Portland cement pastes

Binary systems composed of Portland cement (PC) and calcium sulfoaluminate (CSA) cement have stood out for applications requiring high early strengths. Nevertheless, the application of these systems may be limited due to their properties in the fresh state, which requires a better understanding of the rheological behavior of these materials. Thus, this study evaluated the incorporation of different polycarboxylate-based superplasticizer (SP) contents (0.15, 0.20, and 0.25 wt%) on PC and PC-CSA binary cement pastes. Rotational rheometry, isothermal calorimetry, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption and desorption tests to assess the pore size distribution of cement pastes were conducted. While the SP incorporation reduced the dynamic yield stress of PC pastes, it progressively increased the yield stress of PC-CSA systems. The increase in SP content increased the main heat flow peak of PC-CSA pastes, although it did not significantly affect the cumulative heat after 160 h of hydration. FTIR and XRD confirm higher ettringite contents in the binary systems and indicate the presence of carboaluminates phases after 7 d of hydration in both PC and PC-CSA and hemicarboaluminate in PC-CSA pastes. The CSA incorporation reduced the cumulative pore volume by up to 32% compared to PC pastes, while the SP content evaluated did not significantly affect the porosity of PC-CSA pastes.

Strengthening effect of sulphoaluminate cementitious grouting material for water-bearing broken rocky stratum

A rapid-hardening sulphoaluminate cementitious grouting material (SCGM) is improved for water-bearing broken rocky stratum. Hydroxy propyl methyl cellulose (HPMC) and polycarboxylate-based superplasticizer (PCE) are used to improve fresh-state performance. Main diffusion ability, fresh-state properties, basic mechanical strengths, microstructure, etc., are investigated. A novel grouting simulation apparatus is designed to assess grouting effectiveness, the holistic reinforcement effect, compressive strength and anti-permeability of grouted specimen, typical failure mode, influence of key parameter and bonding characteristic of grout-rock interface are studied. The combination of 0.4 % PCE and 0.02 % HPMC can be applied at water-binder ratio (w/b) of 0.65–1.0. The maximal 3 d and 28 d unconfined compressive strength (UCS) of SCGM are 15.87 and 18.60 MPa, its 28 d UCS of grouted specimen can attain 14.98 MPa. The SCGM is eligible for rapid water blocking and effective reinforcement especially in water-rich and broken rocky strata. Based on the Coulomb failure criterion, relationships among UCS, internal friction coefficient and cohesion of reinforced rock were derived. Based on the linear relationship between internal friction angle (φ) or cohesion (C) and volumetric block proportion (VBP), the quantitative expression with UCS and VBP was established. In comparision with experimental data, feasibility of the quantitative formula in predicting UCS of reinforced rock is proved.

Sonicação de superplastificante à base de policarboxilato para aplicação em matrizes cimentícias

Abstract Sonication is widely used for nanomaterials dispersion in cementitious matrices. Polycarboxylate-based superplasticizer (SP) admixtures are usually incorporated in the aqueous nanomaterials suspension before sonication to improve the dispersion of these materials. Nevertheless, the effect of sonicating SP on its molecular structure or dispersing performance has not been fully investigated. This work assessed the effect of sonicating a commercial SP at 20 kHz, 750 W power, 50 or 80% amplitude, during 15 and 30 min. Initially, the sonication effect was evaluated in aqueous suspension by determining the SP size distribution (through dynamic light scattering – DLS) and zeta potential. Subsequently, the aqueous SP suspensions were used for Portland cement paste production. Rheological tests up to 120 minutes and compressive strength at 14 and 28 days were conducted. DLS and zeta potential results suggested that sonication reduce the size of SP chains. As a result, SP sonication increased the initial dynamic yield stress, viscosity, and hysteresis area of cement pastes. In contrast, SP sonication improved its time-dependent dispersing performance, resulting in pastes with reduced viscosity from 80 minutes onwards. Finally, SP sonication did not affect the compressive strength of cement pastes at 14 and 28 days of hydration. Overall, when SP is sonicated together with nanoparticles for application in cementitious matrices, the effect of sonicating the chemical admixture must be considered when the fresh-state properties of the composite are evaluated.

The Effect of Polycarboxylate-Based Superplasticizers on the Efficiency of Heat Treatment of Monolithic Concrete

The Effect of Polycarboxylate-Based Superplasticizers on the Efficiency of Heat Treatment of Monolithic Concrete

Static and dynamic mechanical thermoanalyses of cement paste with highly dispersed graphene oxide

This study investigated the static mechanical properties of cement pastes with highly dispersed graphene oxide (GO), performed a dynamic mechanical thermoanalysis (DMTA), and studied the microstructure of cement pastes after exposure to high temperatures (105, 200, 300, 450, 600, and 750 °C). First, GO was uniformly dispersed in the cement paste with the aid of polycarboxylate-based superplasticizers. Generally, the incorporation of dispersed GO can enhance the residual compressive strengths of the cement pastes. For pastes with 0.04% GO (by weight) exposed to temperatures of 105, 200, 300, 450, 600, and 750 °C, the strengths are 14.84%, 4.83%, 13.35%, 15.71%, 11.91%, and 64.49% higher than that of pastes without GO, respectively. The DMTA results reveal that cement pastes with 0.04% GO have a high storage modulus and low loss factors in the temperature range of 25–350 °C, which improve their thermal resistance. Moreover, the addition of dispersed GO refines the pore structure and decreases the total porosity at high temperatures by suppressing the coarsening of the pore structure of cement pastes.

Effects and mechanism of superplasticizers and precursor proportions on the fresh properties of fly ash – slag powder based geopolymers

To promote the application of green geopolymer materials, the effects and mechanism of commercial superplasticizers on the fresh properties of one-part geopolymers prepared from fly ash (FA), slag powder (Slag) and anhydrous sodium silicate powder were studied, including flowability, rheological properties and particles packing properties. And the influence of precursor proportion (FA:Slag) i.e. the mass proportion of FA and Slag on the effectiveness of superplasticizers was also considered. The results show the fluidity of geopolymer with 2.4 % liquid naphthalene-based superplasticizer (N-L) increased by 19.20 % when FA:Slag = 85:15, and the 0.20 % one kind of solid polycarboxylate-based superplasticizer (PC-S2) increased the fluidity of geopolymer by 16.47 % when FA:Slag = 95:5. The addition of superplasticizers could improve fluidity, increase plastic viscosity, and decrease yield stress of the pastes. The particles packing properties, including excess water and water film thickness (WFT) of the geopolymer pastes with superplasticizers also increase. It is interesting to find that the effectiveness of superplasticizers varies from different types of superplasticizers. This could be understood by the mechanism of the two types of superplasticizers based on Zeta, FTIR results, and water film theory. Accordingly, naphthalene-based superplasticizers guided by the adsorption-dispersion effect, due to their stable molecular structures and short chains, could improve the workability, while the effectiveness of polycarboxylate-based superplasticizers guided by the steric hindrance effect of lateral chains may be judged by the combined effects of the interaction between particles and the effects induced by superplasticizers.

Reactivity of cemented paste backfill containing polycarboxylate-based superplasticizer

Superplasticizers are used in the preparation of cemented paste backfill (CPB) to improve its rheological properties. CPB produced from sulphide-bearing tailings can generate acid mine drainage (AMD), which has negative environmental impact. The AMD potential can be assessed based on the reactivity of the CPB when exposed to the atmosphere. However, the effect of superplasticizers on the reactivity of CPB is unknown. This paper presents findings from experimental investigations on the effects of polycarboxylate superplasticizers (PCSP) on the reactivity of CPB containing pyrite. The reactivity of cured CPB specimens was determined by monitoring the rate of oxygen consumption in an enclosed chamber. Microstructural tests, namely mercury intrusion porosimetry, X-ray diffraction, and thermogravimetric analyses were also carried out to have a better understanding of the reactive mechanisms. The results obtained show that the addition of PCSP leads to a proportionate reduction of reactivity. The admixture causes the refinement of the pore structure of the CPB by mainly improving binder hydration and self-consolidation. It was also observed that less pyrite crystals were present in the CPB containing the superplasticizer. High curing temperature was also found to improve binder hydration, leading to a decrease in reactivity of CPB with PCSP. Due to the micro-filer effects on the CPB pore structure, partial replacement of cement with fly ash and blast furnace slag also decreases the reactivity of CPB. These research findings will be valuable for the design of cost-effective, more environmentally friendly and sustainable CPB structures.

Influence of superplasticizer on workability and strength of ambient cured alkali activated mortar

Alkali activated materials contain aluminosilicates, which can be used for building with a low environmental impact by repurposing waste resulting in cost-effective construction. The impact of nature and superplasticizer dosage on fly ash slag-based ambient cured mortar activated with sodium silicate and sodium hydroxide is not yet definitive. This paper studies the influence of various superplasticizers on fly ash-based ambient cured mortar activated with sodium silicate and sodium hydroxide. The effect of superplasticizers was evaluated by adding various superplasticizers including melamine, polycarboxylate ether and naphthalene-based superplasticizers in different dosages from 0 to 3% at 0.5% intervals. Fresh properties of alkali-activated mortar with various percentages of superplasticizer were tested using flow table apparatus and compared with mortar without superplasticizer. The hardened property of the alkali-activated mortar was tested by checking the compressive strength of the mortar cube. From the test results, naphthalene and polycarboxylate ether-based superplasticizers are compliant with alkali-activated mortar. Melamine-based superplasticizer shows a slight reduction on strength of alkali-activated mortar. In the ambient cured mortar, the optimum concentration for naphthalene and polycarboxylate ether-based superplasticizers is 2.0 percent, whereas melamine-based superplasticizer exhibits maximum strength for 2.5 percent. Even though naphthalene and polycarboxylate-based superplasticizers are effective for alkali-activated mortar, the most efficient type is the polycarboxylate ether-based superplasticizer.

Enhanced effects of carbon-based conductive materials on the piezoresistive characteristics of cementitious composites

In the present study, an enhanced effects of carbon-based conductive materials on the piezoresistive characteristics of cementitious composites were investigated. A polycarboxylate-based superplasticizer and silica fume were used to disperse conductive mateirals effectively into cement pastes. The dispersion of the conductive materials in the cement pastes was evaluated through electrical resistance measurement, zeta-potential test, and sedimentation test. In this study, carbon nanotube (CNT) and carbonyl iron powder (CIP) were used as conductive materials. The piezoresistive characteristics of the cementitious composites under cyclic loading conditions were explored. The effects of the incorporation of CNT and CIP on the piezoresistive performance were evaluated through the electrical resistance change and the relationship between the electrical resistance change and loads. The test results indicated that the incorporation of CIP into cementitious composites with CNT improved the piezoresistive sensing performance of the composites. The maximum electrical resistance changes of the composites with CIP were 67.49% when the CNT content was 0.5 wt%. Furthermore, the effects of various temperature conditions on the piezoresistive characteristics of cementitious composites were studied. Changes in piezoresistive characteristics of the composites exposed to elevated temperature and subjected to freeze-thaw cycles were analyzed. The electrical resistance change of the conductive network significantly changes at 200 °C.

Physical and mineralogical properties of calcined common clays as SCM and their impact on flow resistance and demand for superplasticizer

Physical properties of calcined clays differ significantly and depend to a large extent on the mineralogy of the raw clays. In this study, four common clays and one kaolinite-rich mine tailing are calcined at 800 °C. Their impact on flow properties of blended cement paste is measured via rotational viscometer and analyzed by (modified) Bingham and Herschel-Bulkley model, combined with the calculation of flow resistance. The demand for superplasticizers rises significantly due to the special characteristics of calcined clays, namely particle size, a high water demand and negative zeta potential. Muscovite present in raw clay is critical as it increases the water demand, yield stress and viscosity. In general, the addition of three industrial polycarboxylate-based superplasticizers (PCEs) reveals good dispersion. Calcined kaolinite-rich clays require more PCE compared to calcined clays rich in 2:1 phyllosilicates. The studied PCEs interact well with all types of metaphyllosilicates besides metamuscovite.

Metakaolin-red mud/carbon nanotubes geopolymer nanocomposite: mechanical properties and structural studies

In this research, the mechanical properties and structural studies of the geopolymer nanocomposite of metakaolin-red mud/carbon nanotubes were investigated. The geopolymer was designed by using metakaolin and red mud as aluminosilicate sources. Red mud replaced between 10 to 30% of the metakaolin. The mass ratio of the solid material and activator liquid was optimized in 1.5:1. Afterward, 1, 2, and 3 wt% multi-wall carbon nanotubes (MWCNTs) were dispersed in a polycarboxylate-based superplasticizer and were added to the geopolymer, which was mixed homogeneously. Geopolymer nanocomposites were characterized by XRD, FTIR, SEM, compressive and flexural strength measurements. The results indicated that the compressive and flexural strengths of the samples increased with curing time. The addition of red mud decreased the compressive and flexural strength of the geopolymer samples due to less reactivity and presence of a non-reactive impurity in red mud. By adding 2% MWCNTs, the compressive and flexural strengths increased to 37.05% and 36.06%, respectively, owing to the crack-bridging mechanism and filling of the cavities and porosity. FTIR spectra demonstrated the growth of the asymmetric stretching vibrations of T–O–Si (T: Si or Al) at approximately 995.85–1083.55 cm−1, confirming the realization of the geopolymerization process in the structure.

Reversible Adsorption of Polycarboxylates on Silica Fume in High pH, High Ionic Strength Environments for Control of Concrete Fluidity.

Polycarboxylate-based superplasticizers are essential for production of ultrahigh-performance concrete (UHPC), facilitating particle dispersion through electrostatic repulsion and steric hindrance. This study examines for the first time the effect of changes in pH, ionic strength, and charge on the adsorption/desorption behavior of a polycarboxylate-based superplasticizer on silica fume in aqueous chemistries common in low-CO2 UHPC. Data from total organic carbon measurements, Fourier transform infrared and nuclear magnetic resonance spectroscopy, and zeta potential measurements reveal the silica surface chemistry and electrokinetic properties in simulated UHPC. Addition of divalent cations (Ca2+) results in polycarboxylate adsorption on silica fume via (i) adsorption of Ca2+ ions on the silica surface and a negative zeta potential of lower magnitude on the silica surface and (ii) reduction of polycarboxylate anionic charge density due to complexation with Ca2+ ions and counter-ion condensation. Addition of OH– ions results in polycarboxylate desorption via deprotonation of silanol groups and a negative zeta potential of greater magnitude on the silica surface. Simultaneous addition of both Ca2+ and OH– results in rapid polycarboxylate desorption via (i) formation of an electric double layer and negative zeta potential on the silica surface and (ii) an increase in polycarboxylate anionic charge density due to deprotonation of the carboxylate groups in the polymer backbone, complexation with Ca2+ ions, and counter-ion condensation. This provides an explanation for the remarkable fluidizing effect observed upon addition of small amounts (1.0 wt %) of a solid, powdered Ca source to fresh, low-CO2, UHPC, which exhibits significantly higher fresh state pH (>13) than those based on Portland cement (pH 11).

Effect of polycarboxylate superplasticizer on hydration and properties of belite ye’elimite ferrite cement paste

Belite-Ye’elimite-Ferrite (BYF) cements have received increasing attention in view of their lower CO2 footprint and their interesting performances. This work deals with the effect of polycarboxylate superplasticizer (SP) on BYF cement paste. It was found that SP dosage must be low in order to avoid destabilization, and thus improve the resistance to bleeding and segregation. Also, the good affinity of polycarboxylate-based superplasticizer with cement surface improves the cement particles dispersion and causes a significant diminution of the yield stress during the low activity period. Furthermore, it is shown that SP causes a delay in the early age hydration, inducing a decrease in the compressive strength at early age while it increases them after 90 days.

Insight into Saturated Hydraulic Conductivity of Cemented Paste Backfill Containing Polycarboxylate Ether-Based Superplasticizer

Recycling of tailings in the form of cemented paste backfill (CPB) is a widely adopted practice in the mining industry. Environmental performance is an important design criterion of CPB structures. This environmental performance of CPB is strongly influenced by its saturated hydraulic conductivity (permeability). Superplasticizers are usually added to improve flowability, but there is a limited understanding of their influence on the hydraulic properties of the CPB. This paper presents new experimental results on the variations of the hydraulic conductivity of CPB containing polycarboxylate-based superplasticizer with different compositions and curing conditions. It is found that the hydraulic conductivity of the CPB decreases with the addition of superplasticizer, which is beneficial to its environmental performance. The reduction is largely attributable to the influence of the ether-based superplasticizer on particles mobility and cement hydration. Moreover, both curing temperature and time have correlations with the hydraulic conductivity of CPB containing superplasticizer. In addition, the presence of sulfate and partial replacement of PCI with blast furnace slag reduces the hydraulic conductivity. The variations are mainly due to the changes in the pore structure of the CPB. The new results discussed in this manuscript will contribute to the design of more environmental-friendly CPBs, which is essential for sustainable mining.

Evaluations of All-in-One, Polycarboxylate-Based Superplasticizer with Viscosity Modifying Agents for the Application of Normal-Strength, High-Fluidity Concrete

High fluidity concrete exhibits an excellent self-compacting property. However, the application of typical high-fluidity concrete is limited in the normal strength range (18~35 MPa) due to the large amount of binder. Therefore, it is important to solve these problems by adding a viscosity modifying agent (VMA) with a superplasticizer (PCE), which helps to improve the fluidity of the concrete. In addition, the rheology and stability of the concrete with VMA can be improved by preventing bleeding and segregation issues. Current studies focused on the physical phenomena of concrete such as the fluidity, rheological properties, and compressive strength of normal-strength, high-fluidity concrete (NSHFC) with different types of a polycarboxylate-based superplasticizer (NPCE). The obtained results suggested that the combinations of all-in-one polycarboxylate-based superplasticizers (NPCE) did not cause any cohesion or sedimentation even stored for a long time. The combination of three types of VMA showed the best fluidity (initial slump flow of 595~630 mm) without any segregation and bleeding, and the compressive strength at 28 days was also found to be the highest: 34–37 MPa. From these results, the combination of PCE (2.0%) + HPMC (0.3%) + WG (0.1%) + ST (0.1%) showed an 18% higher plastic viscosity and -4.4% lower yield stress than Plain.

Effectiveness of common water-reducing admixtures in alkali-activated slag pastes with different types of activator

Rheology of alkali-activated slag (AAS) is a very complex issue, where the activator nature as well as its dose play an important role. Moreover, the use of water-reducing admixtures in these systems is an issue, as they often do not work properly. This could be attributed to the high pH as well as to the surface chemistry of AAS. Therefore, lignosulfonate-, polynaphthalene- and polycarboxylate-based superplasticizers were used to modify AAS pastes with sodium waterglass, hydroxide and carbonate activator. These pastes were tested using a rotational rheometer in an oscillatory shear mode of increasing shear strain to observe the evolution of viscoelastic moduli and to determine the oscillatory stress corresponding to the linear viscoelastic region limit (“yield point”) and to the crossover point, where the storage modulus equals the loss modulus (“flow point”). In most cases, the used plasticizers did not improve the rheological properties; the only exception was the lignosulfonate one in sodium hydroxide-activated slag.