Commercial Admixtures Research Articles

An Investigation on Mineral Dissolution and Precipitation in Cement-Stabilized Soils: Thermodynamic Modeling and Experimental Analysis

Thermodynamic modeling helps to reveal insights into the basic chemical kinetics of dissolution and precipitation in cementitious materials, but relevant applications to cement-stabilized soils have seldom been reported. Based on the thermodynamic database of Cemdata18 and the pore solution composition of cement-stabilized soils, this study formulated a specialized thermodynamic model, using essential thermodynamic constants for soil minerals that were calculated to ensure the model’s accuracy. Two commercial admixtures of alkaline activator and polynaphthalene sulfonate were selected for the different modification mechanisms and plain and modified cement-stabilized soils were prepared. Compressive strength was tested to determine the specimens for pore solution analysis and the influences of the admixture type and dose on dissolution and precipitation were investigated by modeling the ionic activity products and saturation indexes. An X-ray diffraction (XRD) analysis was performed to verify and complement the thermodynamic results. The major research findings were that (1) thermodynamic modeling can be reliably applied to cement-stabilized soils by providing the essential thermodynamic data and an appropriate product model, (2) the pozzolanic reaction is accelerated by increasing the OH− concentration in the pore solution, while the cement hydration is highly dependent on the dissolution of Ca(OH)2 and the relevant complexes and (3) the dissolution equilibrium of Ca(OH)2 is directly affected by the alkaline activator dissolution and is indirectly affected by the polynaphthalene sulfonate adsorption of the reactants.

The effect of silanes as integral hydrophobic admixture on the physical properties of cement based materials

The paper explores the possibility of using organosilicon compounds (e.g., poly(dimethylsiloxane) and triethoxyoctylsilane) in commercial admixtures as internal hydrophobization agents for porous cement-based materials. The study involved the cement mortar with five different hydrophobic admixtures. Four of them is based on triethoxyoctylsilane, but with various concentration of the main ingredient, and one of them on poly(dimethylsiloxane). Mechanical properties, capillary water absorption, as well as microstructure were investigated. The organosilicon admixtures efficiently decrease the capillary water absorption even by 81% decreasing mechanical strength of cement mortar at the same time even by 55%. Only one admixture, based on poly(dimethylsiloxane) caused significant changes in microstructure of cement mortar.

Effects of Black Scoria on Mechanical Properties and Thermal Insulation Properties of Building Materials

The effect of fine black scoria on the mechanical properties and thermal conductivity of building materials was investigated in this study. Black scoria was used to replace cement in concrete with various percentages. Four concrete samples containing 0%, 10%, 20%, and 30% black scoria were prepared. Characterization black scoria was performed via X-ray powder diffraction, X-ray fluorescence, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry analysis. Then, the compressive strength of the samples was investigated after 14, 21, 28, and 91 days of curing at room temperature. Finally, the thermal conductivities of the samples were measured after 28 days. Based on the experimental results, the highest compressive strength among the samples was 45.3 MPa, obtained from the mixture containing 10% black scoria after 91 days of curing. It was also observed that the average thermal conductivity of the concrete samples decreased with an increase in the fine black scoria content from 1.8 to 0.193 W m−1 K−1. Thus, black scoria is an appropriate substitute for commercial admixtures in cement composites in thermally insulating building materials due to its low density, excellent compressive strength, and good heat insulation properties.

Mechanical and electrical properties of MWCNTs - high early strength cement - mortars composite: Dispersion of CNTs and effect of chemical admixtures.

The objectives of this research were to study (1) the dispersion of MWCNTs in an aqueous system by three commercial admixtures (CAds) for concrete, and (2) the effect of CAds and MWCNTs on indirect tensile strength and electrical conductivity of MWCNTs-high early strength (HE) cement-mortar composites. To achieve the objectives, we dispersed MWCNTs in an aqueous system with (1) hydroxylated polymers-based water reducing plasticizer (HPs), a nonionic compound, (2) Naphthalene based superplasticizer (SNF), an anionic compound, and (3) calcium chloride-based accelerating agent (CC) a neutral amphoteric salt. We prepared a total of 242 samples grouped in three sets: (1) Plain mortar [PM] (water + HE cement + Sand), (2) [PM+CAd], and (3) [PM+CAd+MWCNTs]. The three CAds dispersed MWCNTs in an aqueous solution. The CC and HPs admixtures have a two-time bigger dispersing power than the SNF. They demand half of SNF's ultrasound energy for optimal dispersion. Although the SNF (anionic) based superplasticizer resulted incompatible with the HE cement, it improved the indirect tensile strength of [PM+SNF+MWCNTs] composite. In contrast, the CC (amphoteric) based accelerating agent was compatible with the HE cement; the CC adsorption on the MWCNTs surface favors an improvement in the electrical conductivity of [PM+CAd+MWCNTs] composite.

Admixture tuning for high‐performance concrete for the production of novel precast pre‐stressed long‐span girders for highway overpasses

AbstractThe improvements observed in concrete technology in the last decades, namely the production of Portland cement CEM I 52.5 R, the development of third generation super‐plasticizers, and the commercialization of additions with high pozzolanic properties, turned possible the development of new concrete products using high performance concrete (HPC). Nevertheless, their implementation in the production process of the conservative precast concrete industry is not yet a reality. In this paper, the development and characterization of a HPC exhibiting high workability in the fresh state and high compressive strength in hardened state is presented. This HPC aims at producing, on a competitive basis, precast pre‐stressed long‐span girders for highway overpasses. For this reason, the main goal was to maximize the abovementioned properties but using the constituents available at the concrete precast company supporting the research. A set of different commercial admixtures was gathered and their influence on both compressive strength and workability of concrete was experimentally investigated. Results show that the compatibility between the admixture and the cementitious material is of paramount importance. By selecting the best type of the considered super‐plasticizers and by optimizing its dosage, it was possible to increase the workability from class S1 to S5 and, simultaneously, increase the compressive strength in circa 50%, up to 120 MPa, at 28 days of age.

Sustainable cement with Al-anodizing waste: Evaluating reactivity and feasibility as a shrinkage-compensating admixture

The Al-anodizing waste (AAW) is generated in large amounts from the aluminum anodizing process and is often discarded in landfills. This work proposes a novel and economic recycling route for Al-anodizing waste (AAW) as a shrinkage-compensating admixture (SCA) for Portland cement matrices. The usage of SCA has been shown as an effective way to combat the excessive shrinkage of concrete, which can result in cracking. Most of the commercial admixtures are based on the formation of additional ettringite, inducing expansion in concretes and compensating the later shrinkage. Since commercially available admixtures are relatively expensive, we aim to produce a low-cost and eco-friendly SCA by using AAW. Interactions between waste and cement were extensively investigated in aqueous suspensions by electrical conductivity, mass spectroscopy and modified Chapelle test and in cement pastes by thermogravimetry, isothermal conduction calorimetry, X-ray diffraction, and scanning electron microscopy. Results revealed a strong reactivity between waste and hydrated cement evidencing the consumption of calcium and sulfate and the formation of numerous nuclei of nanocrystals of ettringite. Preliminary shrinkage/expansion tests confirmed the feasibility of using the AAW for such application.

Effect of Fineness of Basaltic Volcanic Ash on Pozzolanic Reactivity, ASR Expansion and Drying Shrinkage of Blended Cement Mortars.

This study focuses on evaluating the effect of the fineness of basaltic volcanic ash (VA) on the engineering properties of cement pozzolan mixtures. In this study, VA of two different fineness, i.e., VA fine (VF) and VA ultra-fine (VUF) and commercially available fly ash (FA) was used to partially replace cement. Including a control and a hybrid mix (10% each of VUF and FA), eleven mortar mixes were prepared with various percentages of VA and FA (10%, 20% and 30%) to partially replace cement. First, material characterization was performed by using X-ray florescence (XRF), X-ray powder diffraction (XRD), particle size analysis, and a modified Chappelle test. Then, the compressive strength development, alkali silica reactivity (ASR), and drying shrinkage of all mortar mixes were investigated. Finally, XRD analysis on paste samples of all mixes was performed to assess their pozzolanic reactivity at ages of 7 and 91 days. The results showed increased Chappelle reactivity values with an increase in the fineness of the VA. Mortars containing high percentages of VUF (20% and 30%) showed almost equal compressive strength compared to corresponding FA mortars at all ages, however, the hybrid mix (10% VUF + 10% FA) exhibited higher strength than that of the reference mix (100% cement), particularly, at 91 days. At low percentages (10%), ASR expansion in both VF and VUF mortars was higher compared to the corresponding FA mortar and the opposite behavior was observed at high percentages (20% and 30%). Among all the mixes including the control, mortar with VUF was found to be most effective in controlling drying shrinkages at all ages. The rate of consumption of calcium hydroxide (Ca(OH)2) for pastes containing VUF and FA was almost the same, while VF showed low Ca(OH)2 intensity. These results indicate that an increase in the fineness of VA significantly improvs performance, and therefore, it could be a feasible substitute for commercial admixtures in cement composites.

Influence of Polymer Admixtures on the Rheological Properties and Heat of Hydration of Alkali Activated Slag Pastes

The purpose of this study is to investigate the rheological properties of alkali-activated slag prepared as a paste modified by various amount of polymer admixtures. Four commercial admixtures VINNAPAS® 5023 L, 5111 L, 7016 F and 7220 E were used as polymer admixture in this study. These admixtures were incorporated to alkali activated slag pastes in quantities between 0.5 and 2% by mass of slag. Rheological properties as shear stress and viscosity of fresh pastes were examined by Discovery HR-1. Another main focus of this paper is the effect of selected admixtures on the heat of hydration of an alkali activated slag. Results indicate that addition of polymer admixtures affects the viscosity of the pastes and hydration process.

Stability of Polymer Admixtures in Alkaline Media

Nowadays alkali activated binders are one of alternative materials to Portland cement. Alkaline activation is a process when the material hardens in medium at pH>12. This paper presents the study of stability of different polymer admixtures (polypropylene glycol, polyvinyl alcohol, polyethylene glycol with different molecular weight, different modifications of commercial polymer admixtures VINNAPAS® and shrinkage-reducing Peramin SRA) in alkaline media NaOH at pH=12.42. The influence of the alkaline medium on the properties of polymer admixtures was examined by infrared spectroscopy. All types of VINNAPAS®, Peramin SRA are unstable in high alkaline media.

Design of masonry mortars fabricated concurrently with different steel slag aggregates

The simultaneous application of electric arc furnace slag and ladle furnace white slag, in substitution of natural fine aggregate in masonry mortars, is presented with the principal objective of achieving mixes that show a similar performance to conventional mortars. Materials dosed with steel slag fines at different levels of substitution (25%, 50%, 75% and 100%) were designed, employing commercial admixtures in the samples. A comparative study of the most significant mortar properties is conducted, such as workability, adhesiveness, water retentivity and mechanical strength, between the mortars prepared with natural fine aggregate and those manufactured with additions of slag. The results indicate that technically viable mortars may be obtained for their use in construction and building, which thereby achieve the reuse and valorization of waste products that would otherwise be disposed of in landfill sites.

An Application of Computer‐Aided Molecular Design (CAMD) Using the Signature Molecular Descriptor–Part 2. Evaluating Newly Identified Surface Tension‐Reducing Substances for Potential Use as Shrinkage‐Reducing Admixtures

In this study, the use of computer‐aided molecular design (CAMD) is validated as a tool for enabling the discovery of new shrinkage‐reducing compounds for possible use in portland cement composites and is framed as one of many multiscale modeling tools in a broad hierarchy of possibilities. Twelve additives were tested for their ability to inhibit shrinkage in Type I ordinary portland cement under both autogenous and drying conditions. The 12 additives included two commercial shrinkage‐reducing admixtures (SRAs), two active ingredients of a commercial admixture [one of which was used to establish the quantitative structure–property relationships (QSPR)], two additional classified as potential SRA compounds based on the patent literature, four newly identified compounds predicted by using CAMD and an inverse quantitative structure–property relationship (I‐QSPR), and two other compounds use to establish the QSPR relationship. The newly identified I‐QSPR compounds were targeted for their ability to reduce the surface tension of water, a primary consideration for shrinkage‐reducing activity. Results for both drying shrinkage and autogenous shrinkage indicate that the designed compounds perform similar to commercial admixtures, yet have different chemical functionalities. Hydration data and set measurements were also considered since selection of new SRAs is a multiparameter problem with many constraints. Thus, these newly identified shrinkage‐reducing compounds can potentially provide additional options for use in portland cement concrete applications.

Role of organic admixtures on thaumasite precipitation

Thaumasite formation is normally a slow process; however some studies have shown that the presence of sucrose promotes its formation substantially. Many of today's concretes contain organic admixtures and no research has been conducted to date to determine whether the presence of these admixtures may induce or favour thaumasite formation. The present study aimed to ascertain whether, like sucrose, admixtures may further that process, and to propose a working methodology to do so.The methodology used was: mixing sodium carbonate, sulfate and silicate solutions with a CaO solution with eleven commercial admixtures. The precipitates obtained after different curing times (up to 1year) and temperatures (5 and 25°C) were characterised with FTIR and XRD.It was possible to distinguish between admixtures that did and those that did not favour thaumasite formation, i.e., products containing lignosulfonates or a mix of sodium carboxylate and polysulfonate as well as aluminium-based accelerating admixtures favoured thaumasite formation.

Strength and workability of masonry mortars manufactured with ladle furnace slag

Ladle furnace basic slag (LFS) is a by-product of the steelmaking process. It has rarely been recovered in the past and is usually disposed of in landfill sites. Despite containing stable chemical substances of great quality, some of which are potentially hydraulic, its practical applications have been limited. This paper discusses the attractive option of using LFS in the manufacture of masonry mortars for use in the construction industry, which requires an analysis of the principal characteristics of such mortars, i.e. workability and mechanical strength. It reports on a comparative study, using standard commercial admixtures, between conventional masonry mortars and mortars manufactured with LFS as a partial replacement for sand and cement, the results of which imply considerable economic savings in sand and cement, improvements in the properties of the mortars and in overall sustainability, by avoiding disposal and conserving natural resources.

Techniques and methods of characterization of admixtures for the concrete

Admixtures are defined as those products that are incorporated in the moment of the process of mixture of the concrete in a quantity not bigger than 5 by mass of the cement %, with relationship to the cement content in the concrete, with object of modifying the properties of the mixture in .state fresh and/or hardened. The behaviour of the admixtures depends on its chemical and ionic composition, the organic functional groups present, and the structure of the polymer and the distribution of molecular weight of the different polymers. In the present work the techniques and methods of characterization physical-chemistry, chemistry and ionic, structural, as well as of the polymers that constitute this admixtures, are described. A lot of techniques have been employed like: ionic chromatography, ultraviolet-visible spectroscopy (UV-VIS), Fourier transform infrared spectroscopy (FTIR), Fourier transform Raman spectroscopy (FT-Raman), nuclear magnetic resonance spectroscopy ( 1 H-RMN and 13 C-RMN), gel permeation chromatography (GPC). Two commercial admixtures have been selected to carry out this characterization, a superplastificant based on policarboxilates, and a reducer of the shrinkage based on polipropilenglycol.

Strength and Durability of Concrete Containing Salts of Alkenyl-Succinic Acid

The performance of concrete is judged by many different properties, including durability and strength. Admixtures are frequently used to improve these properties. Most admixtures provide a positive effect on only one property and, therefore, combinations of admixtures must be used. Deterioration due to reinforcement corrosion is likely the most important durability issue with reinforced concrete. Corrosion inhibitor admixtures are commonly added to concrete to suppress or delay reinforcement corrosion, and additional admixtures must be added to improve the concrete's freeze-and-thaw resistance. This paper presents research on 2 forms of a chemical that improves the durability of concrete in several ways: by improving corrosion resistance; by reducing water penetration; and by providing resistance to freezing and thawing. The effect of the chemical on several concrete material properties is also discussed. Performance was compared with concrete containing commercial admixtures.

Corrosion Tests with Concrete Containing Salts of Alkenyl-Substituted Succinic Acid

Normally, alkaline cement paste protects steel reinforcement from corroding by facilitating the formation of a thin passive film on the steel. However, chloride ions from deicing salts can migrate through hardened concrete and allow corrosion to occur even in an alkaline environment. The ideal concrete corrosion protection system would be cost-effective and would prevent corrosion for the service life of the structure; however, this ideal solution is not yet available. Corrosion inhibitor admixtures are a good choice to delay reinforcement corrosion because of their nonskill-dependent usage and low maintenance requirements. This research studied a chemical that improved concrete durability in several ways: by improving corrosion resistance; by reducing water penetration; and by providing freeze-and-thaw resistance. Two variations of this chemical, described as alkali metal and ammonium salts of an alkenyl-substituted succinic acid, were used in 48 weeks of corrosion testing on reinforced concrete using linear polarization methods. Performance was compared with concrete cast using commercial admixtures. The results of this research, which should be of interest to state departments of transportation, engineers, material suppliers, and material developers, are provided and discussed.

Corrosion Testing of Grout for Posttensioning Ducts and Stay Cables

Grout mixes using commercially available antibleed admixtures were tested for fresh properties and subsequently corrosion tested using anodic polarization to accelerate the corrosion process. Commercial admixtures that are intended to improve the corrosion protection provided by the grout were also tested in grout mixes containing the antibleed admixture. From a comparison, it was found that the antibleed admixture reduced the corrosion protection of the grout and a mix with no antibleed admixture did not. It was also found that one corrosion protection admixture improved protection while the other admixture reduced protection provided by the grout. Because the accelerated tests were conducted at an artificially high potential of 600 mV, there is some concern that the polarization level at the strand will differ significantly among grouts with varying ohmic resistances. Potentiodynamic tests were conducted on selected specimens, to investigate this effect, and were inconclusive. Further study into this effect is recommended before the higher polarization levels are used to evaluate grouts that having varying ohmic resistances.

98/00330 Interactions of carbon-containing fly ash with commercial air-entraining admixtures for concrete

98/00330 Interactions of carbon-containing fly ash with commercial air-entraining admixtures for concrete

Admixtures in cement: a study of dosage rates on early hydration

The authors have shown from earlier work that the electrical response of cement paste to an alternating electrical field can be used as a technique for monitoring hydration and phenomena such as setting and hardening. This paper demonstrates an area in which the technique could prove effective, by showing the influence of a range of commercial admixtures on electrical response. It is clearly indicated that admixtures have a definite effect on the response characteristics.