Mechanistic quantification of performance loss of PCE superplasticizer in carbonate-enriched cementitious suspensions

Synergetic effect of viscosity modifying admixtures and polycarboxylate ether superplasticizer on key characteristics of thixotropic UHPC for bonded bridge deck overlay rehabilitation

The effect of superplasticizers on rheology and early hydration kinetics of rice husk ash-blended cementitious systems

A study on the interactions between polycarboxylate ether superplasticizer and montmorillonite

A variety of polycarboxylate ether (PCE)-based superplasticizers are commercially available. Their influence on the rheological retention and slump loss in respect of concrete differ considerably. Fluidity and slump loss are the cardinal features responsible for the quality of concrete. These are related to the dispersion of cement particles and the hydration process which are greatly influenced by type of polycarboxylate ether (PCE)-based superplasticizers. On the backdrop of relatively less studies in the context of rheological retention of high strength self-consolidating concrete (HS-SCC), the experimental investigations were carried out aiming at quantifying the effect of the six different PCE polymers (PCE 1-6) on the rheological retention of HS-SCC mixes containing two types of Ordinary Portland Cements (OPC) and unwashed crushed sand as the fine aggregate. The tests that were carried out included T500, V-Funnel, yield stress and viscosity retention tests. The supplementary cementitious materials such as fly ash (FA) and micro-silica (MS) were also used in ternary blend keeping the mix paste volume and flow of concrete constant. Low water to binder ratio was used. The results reveal that not only the PCEs of different polymer groups behave differently, but even the PCEs of same polymer groups also behave differently. The study also indicates that the HS-SCC mixes containing PCE 6 and PCE 5 performed better as compared to the mixes containing PCE 1, PCE 2, PCE 3 and PCE 4 in respect of all the rheological tests. The PCE 6 is a new class of chemical admixtures known as Polyaryl Ether (PAE) developed by BASF to provide better rheological properties in even in HS-SCC mixes at low water to binder mix. In the present study, the PCE 6, is found to help not only in reduction in the plastic viscosity and yield stress, but also provide good rheological retention over the period of 180 minutes. Further, the early compressive strength properties (one day compressive strength) highly depend on the type of PCE polymer. The side chain length of PCE polymer and the fineness of the cement considerably affect the early strength gain.

On the action mechanism of phosphate-based superplasticizers in one-part alkali-activated slag

The conformation in aqueous solution and the adsorption ability to water molecules of polycarboxylate ether (PCE) superplasticizer have important effects on its the properties. In this work, molecular dynamics (MD) simulations were employed to investigate the conformation of PCE molecules and the interaction between PCE and water molecules at microscopic level. Five kinds of PCE molecular models (PCE-2, PCE-6, PCE-10, PCE-14 and PCE-18) with different lengths of main chain were constructed, and the simulation results show that the longer length of main chain makes PCE molecules more stretched. The steric hindrance of PCE enhances from PCE-2 to PCE-14, and then declines from PCE-14 to PCE-18, which result from the greater molecules aggregation. The radial distribution functions (RDFs) indicate that the water absorption capacity of PCE molecule enhanced with the increasing of main chain length, and main chain plays an important role of water molecule capture. Both steric hindrance and water absorption capacity of PCE molecules can effectively affect the diffusion properties of water molecules, and prevent water molecules from contacting with cement particles, which retards the hydration process of cement.

Magneto-rheology control, by means of adding magnetizable particles and applying magnetic field, is a potential approach to satisfy the contradicting requirements of fresh properties in different casting processes. Polycarboxylate ether (PCE) superplasticizer is an essential component of modern cement-based materials, which significantly affects the viscoelastic properties of cementitious suspensions, and hence the movement and distribution of magnetic particles after applying an external magnetic field. This present research focuses on the following two aspects: whether highly flowable cementitious paste containing both magnetic particles and PCE shows rheological response to an external magnetic field, and if yes, is there a difference of magneto-responsive structural evolution of cementitious pastes with and without PCE? For these purposes, the magneto-responsive structural build-up of highly flowable cementitious pastes with various magnetic particles (two nano-Fe3O4 particles and one magnetic fly ash) in the presence of PCE, described by the evolution of storage modulus over time, is evaluated. Experimental results show that highly flowable cementitious pastes containing both magnetic particles and PCE indeed exhibit obvious magneto-rheological (MR) responses. The incorporation of PCE significantly increases the relative MR effect while slightly decreases the absolute MR effect. By comparing the magneto-responsive structural build-up of cementitious pastes with and without PCE, it is revealed that the application of an external magnetic field to a highly flowable cementitious paste with PCE mainly plays a significant role in the increase of solid-like properties.

Conventional concrete does not have durability and higher strength as produced by high performance concrete (HPC). It is known that the HPC possess the following three properties which are high workability, high strength, and durability. The introduction of polycarboxylate ether (PCE) superplasticizer was proved to enhance the workability of concrete even though at a lower water to cement ratio. The study was conducted to find the optimum dosage of PCE and to compare its compressive strength, physical characteristics and morphology of the HPC. The result of the test shows that the high performance concrete (HPC) with addition of 0.5% polycarboxylate ether (PCE) superplasticizer of the cement mass have the highest compressive strength and excellent physical properties.

Clay tolerant superplasticizers can enable the use of low quality, clay containing aggregates and also alleviate the need for washing clay containing sand used in concrete fabrication, thereby promoting sustainable concrete production. Previous studies considered specific aspects of polycarboxylic ether (PCE) superplasticizer molecular design which influence their clay tolerance. In this study, the effect of a combination of various aspects of PCE molecular design on their clay tolerance was investigated. The aim of the study was to determine PCE structural differences that are more tolerant to clay contamination of sands used in concrete making. The objective was to evaluate the effectiveness of six recently developed proprietary PCEs with varying molecular designs in concretes fabricated with clay containing sands sampled from three South African quarries. The PCEs were evaluated by their ability to retain good workability and compressive strength in concretes fabricated using a standard laboratory clay free sand and high clay content sands from the three quarries. Workability was evaluated through slump flow tests and the compressive strength was evaluated through 24 h and 28 d compressive strength tests. Incorporation of an acrylic based PCE with low side chain graft ratio and long side chain lengths in the concretes resulted in a higher initial slump flow of at least 200 mm at 5 min, indicating relatively good workability, which however deteriorated rapidly in concretes made with the clay contaminated sands. Unexpectedly, the 28 d compressive strengths of concretes fabricated with higher clay content sands were found to be comparable to the compressive strengths of concretes made with the clay free standard sand when three of the PCEs were used. High compressive strength in the concretes fabricated with the sand containing the most clay was accomplished by incorporating a PCE with very high molecular weights, very long side chain lengths and a low graft ratio.

Dot gain is different when dots are printed alone, printed in superposition with one ink or printed in superposition with two inks. In addition, the dot gain may also differ depending on which solid ink the considered halftone layer is superposed. In a previous research project, we developed a model for computing the effective surface coverage of a dot according to its superposition conditions. In the present contribution, we improve the Yule-Nielsen modified Neugebauer model by integrating into it our effective dot surface coverage computation model. Calibration of the reproduction curves mapping nominal to effective surface coverages in every superposition condition is carried out by fitting effective dot surfaces which minimize the sum of square differences between the measured reflection density spectra and reflection density spectra predicted according to the Yule-Nielsen modified Neugebauer model. In order to predict the reflection spectrum of a patch, its known nominal surface coverage values are converted into effective coverage values by weighting the contributions from different reproduction curves according to the weights of the contributing superposition conditions. We analyze the colorimetric prediction improvement brought by our extended dot surface coverage model for clustered-dot offset prints, thermal transfer prints and ink-jet prints. The color differences induced by the differences between measured reflection spectra and reflection spectra predicted according to the new dot surface estimation model are quantified on 729 different cyan, magenta, yellow patches covering the full color gamut. As a reference, these differences are also computed for the classical Yule-Nielsen modified spectral Neugebauer model incorporating a single halftone reproduction curve for each ink. Taking into account dot surface coverages according to different superposition conditions considerably improves the predictions of the Yule-Nielsen modified Neugebauer model. In the case of offset prints, the mean difference between predictions and measurements expressed in CIE-LAB CIE-94 ΔE 94 values is reduced at 100 lpi from 1.54 to 0.90 (accuracy improvement factor: 1.7) and at 150 lpi it is reduced from 1.87 to 1.00 (accuracy improvement factor: 1.8). Similar improvements have been observed for a thermal transfer printer at 600 dpi, at lineatures of 50 and 75 lpi. In the case of an ink-jet printer at 600 dpi, the mean ΔE 94 value is reduced at 75 lpi from 3.03 to 0.90 (accuracy improvement factor: 3.4) and at 100 lpi from 3.08 to 0.91 (accuracy improvement factor: 3.4).

Effect of molecular structure of polycarboxylate ether superplasticizer on its tolerance to montmorillonite

In this study, the impact of the molecular weight of isoprenol ether-based (IPEG) polycarboxylate superplasticizers on the dispersing effectiveness in sodium hydroxide-activated slag binder and slag composite cement was investigated. For this purpose, a series of IPEG polycarboxylate ether (PCE) superplasticizers possessing the same anionicity and the same side chain length but varying molecular weights (13,000–400,000 Da) were prepared. The synthesized PCE polymers were then subjected to application-related tests. It was found that their dispersing capacity in the AAS binder differed significantly and that IPEG PCE polymers possessing higher molecular weight generally were more effective. Surprisingly, it was also noticed that in the slag composite cement (90% slag, 10% OPC), generally, higher doses of the PCEs were required than in the OPC-free AAS binder system. Moreover, the working mechanism behind the enhanced dispersing ability of high Mw IPEG PCEs was studied via adsorption and adsorbed layer thickness (ALT) measurements. To determine the ALT of the adsorbed PCE polymers, phosphate-modified polystyrene nanoparticles were selected as a model substrate. Results from dynamic light scattering revealed that high Mw PCEs produce thicker adsorbed layers, which highly benefits the dispersing power of the PCE polymers stemming from enhanced steric hindrance. Finally, different models for the adsorbed conformations of those IPEG PCEs are proposed based on their individual molecular characteristics.

Properties of sulfoaluminate cement-based grouting materials modified with LiAl-layered double hydroxides in the presence of PCE superplasticizer

The effect of sodium tripolyphosphate (STPP) on the fluidity of cement paste with lignin sulfonate (LS), sulfonated naphthalene formaldehyde condensate (FDN) and polycarboxylate ether (PCE) superplasticiser (SP) was studied. The adsorption amounts of LS, FDN and PCE were assessed using UV spectrophotometry and total organic carbon analysis; the concentration of Ca2+ions in solution and the adsorption amounts of STPP were tested with plasma emission spectrometry and the electrokinetic properties of the cement particles were confirmed using ζ-potential measurements. Based on analysis of the adsorption amounts, the Ca2+concentration, ζ-potential and fluidity of cement paste, the competitive adsorption between SPs and STPP was investigated. The result shows that SP and STPP can all adsorb onto the surface of cement particles and there is competitive adsorption between STPP and SP. STPP prevents Ca2+releasing and pre-empts the adsorption sites of SP; it causes a reduction in the adsorption amount of SP and increases the ζ-potential of cement particles. The SP also reduces the adsorption amount of STPP. Competitive adsorption causes changes in fluidity and fluidity loss. STPP can improve the initial fluidity and reduce fluidity loss of cement paste with LS or FDN. With PCE and STPP, the initial fluidity can be improved, but fluidity loss increases; this is due to the different molecular structure of the SPs. It is thus suggested that STPP can be used with LS and FDN to improve fluidity and reduce fluidity loss, but it is a disadvantage when used with PCE.

Amphoteric polycarboxylate superplasticizers with enhanced clay tolerance: Preparation, performance and mechanism