Effect of Polyacrylic Acid on Rheology of Cement Paste Plasticized by Polycarboxylate Superplasticizer

The Effects of Hydroxypropyl Methyl Cellulose and Metakaolin on the Properties of Self-Compacting Solidified Soil Based on Abandoned Slurry

As a new type of backfill material, Self-compacting solidified soil (SCSS) takes the abandoned slurry of cast-in-place piles after dewatering and reduction as the main raw material, which brings a problem of coordinating the working performance with the mechanical property under the condition of high mobility. In this paper, hydroxypropyl methyl cellulose (HPMC) and metakaolin were introduced as additives to solve this problem. First, the workability and mechanical properties of SCSS were regulated and optimized by means of the water seepage rate test, the flowability test, and the unconfined compressive strength test. Second, this study also used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the effects of HPMC and metakaolin on the physical phase and microstructure of SCSS. In this way, the results showed that there was a significant impact on the flowability of SCSS, that is, when the dosage reached 0.3%, the water seepage rate of SCSS was reduced to less than 1%, and the compressive strength at 7 days reached its peak. At the same time, HPMC weakened the strength growth of SCSS in the age period of 7 days to 14 days. However, the addition of metakaolin promoted its compressive strength. XRD analysis showed that the additives had no significant effects on the physical phases. And, from the SEM results, it can be seen that although the water-retaining effect of HPMC makes hydration of cement more exhaustive, more ettringite (AFt) can be observed in the microstructure. In addition, it can be observed that the addition of metakaolin can generate more hydrated calcium silicate (C-S-H) due to the strong surface energy possessed by metakaolin. As a result of the above factors, SCSS filled the voids between particles and improved the interface structure between particles, thus enhanced the compressive strength.

Influence of Pentaerythritol Tetraacrylate Crosslinker on Polycarboxylate Superplasticizer Performance in Cementitious System

In this work, a crosslinked polycarboxylate superplasticizer (crosslinked-PC) was synthesized via the free radical polymerization reaction. Pentaerythritol tetraacrylate (PETA) was used as the crosslinked agent. A comparative comb-like polycarboxylate superplasticizer (comb-like-PC) was prepared under the same reaction conditions. The dispersion retention capacity, dispersion capability, hydration characteristics of the cement paste and setting time were investigated in detail. At the dosage of 0.6% bwoc, the fluidity of the cement/crosslinked-PC paste was about 340 mm, which was 40~50 mm larger than the cement/comb-like-PC paste. The dispersion retention capacity of the cement/crosslinked-PC paste was observed to be much superior due to higher adsorbed amounts on the cement particles. Moreover, the cement/crosslinked-PC paste exhibited the initial and final setting durations of 196 and 356 min, respectively, which indicated an enhancement of 18 and 68 min compared to the cement/comb-like paste. The crosslinked copolymers exhibit a stronger retardation effect than the comb-like copolymers due to their enhanced adsorbed amounts and stronger steric hindrance effect. This is further illustrated by the characterization of the hydration process and hydration products. It can be concluded that it is feasible to improve the dispersive capacity and the dispersion retention capacity of PC by changing the molecule structure from comb-like to slightly crosslinked.

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.

Combination of Polymeric Superplasticizers, Water Repellents and Pozzolanic Agents to Improve Air Lime-Based Grouts for Historic Masonry Repair

This paper presents the experimental procedure to develop air lime-based injection grouts, including polymeric superplasticizers, a water repellent agent and pozzolanic agents as additives. Our research focuses on the development of grouts to improve various characteristics simultaneously by combining different additions and admixtures. Aiming to improve the injectability of the grouts, in this study, different polymeric superplasticizers were added, namely polycarboxylated-ether derivative (PCE), polynaphthalene sulfonate (PNS) and condensate of melamine-formaldehyde sulfonate (SMFC). As a water-repellent agent, sodium oleate was used to reduce the water absorption. The enhancement of the strength and setting time was intended by using microsilica and metakaolin as pozzolanic mineral additions. Compatibility between the different admixtures and action mechanism of the different polymers were studied by means of zeta potential and adsorption isotherms measurements. Diverse grout mixtures were produced and investigated by assessing their injectability, fluidity, stability, compressive strength, hydrophobicity and durability. This research led to several suitable mixtures produced by using more than one component, to enhance efficiency and to provide better performance of grouts. According to the results, the grout composed of air lime, metakaolin, sodium oleate and PCE was found to be the most effective composition, improving the mechanical strength, injectability and hydrophobicity.

Effect of sodium gluconate on molecular conformation of polycarboxylate superplasticizer studied by the molecular dynamics simulation

Sodium gluconate (SG) has been accepted as one of the main additional components in polycarboxylate superplasticizer (PCE) system, due to its excellent retarding effect. While the negative effect on dispersion of PCE was reported in the literature, the reason was not completely revealed. In this study, molecular dynamics simulation was used to investigate the mutual influence between SG and PCE in calcium hydroxide (CH) solution. Radial distribution function (RDF) was used to analyze the effects of SG on the complexation of PCE with Ca²⁺. Radius of gyration (Rg) was adopted to characterize the conformations of the backbone and side chains of PCE in CH solution. Finally, several adsorption and dispersion models were proposed. The results showed that the presence of SG would perturb adsorption of PCE, which was one of the main reasons that affected the dispersion ability of PCE. SG could preferentially combine with Ca²⁺ so that less amount of Ca²⁺ is available for combination of PCE, and this could extend the main chain of PCE and show advantage for PCE adsorption. Besides, adding SG could squeeze the side chains of PCE, which would put a negative effect on the dispersion. These findings gave deeper insight into understanding the dispersion mechanism of PCE-SG system.

Special Issue of Environment-Friendly Construction Materials

This special issue, “Environment-Friendly Construction Materials”, has been proposed and organized as a means to present recent developments in the field of construction materials. For this reason, the articles highlighted in this editorial relate to different aspects of construction materials, from pavement materials to building materials, from material design to structural design, from self-healing to cold recycling, from asphalt mixture to cement concrete.

Rheological Behavior of Fresh Cement Pastes

Rheology of a concrete is mainly controlled by the rheological behavior of its cement paste. This is the main practical reason for the extensive research activity observed during 70 years in this research subfield. In this brief review, some areas of the research on the rheological behavior of fresh cement pastes (mixture method influence, microstructure analysis, mineral additions influence, chemical additives influence, blended cements behavior, viscoelastic behavior, flow models, and flow behavior analysis with alternative methods) are examined.