Set-retarding Admixtures Research Articles

Effect of Set-retarding Admixtures on Properties of Slurry for Non-reactive Mold Slag of High-Aluminum Steel

Effect of Set-retarding Admixtures on Properties of Slurry for Non-reactive Mold Slag of High-Aluminum Steel

Novel application of potassium methylsiliconate in cement-based materials: Retarding of hydration process and improvement of compressive strength

The presented research investigates the application of the organosilicon compound named potassium methylsiliconate (MESI) as a set-retarding admixture for cement-based materials which also provides the strengthening effect. The study concerns the impact of three dosages of MESI (1%, 2% and 3% per cement mass) on the properties of the cement paste, mortar and concrete. The greatest delay of the setting time of cement CEM I 42.5 R and retardation effect, examined by manual Vicat apparatus, was observed for addition of 1% methylsiliconate. The beginning of the setting was prolonged to 23 h. The influence of potassium methylsiliconate on the kinetics of cement hydration was investigated by isothermal calorimetry. The calorimetric results disclosed significant extension of induction period during Portland cement hydration with addition of potassium methylsiliconate as an admixture. It is especially visible in case of addition of 1% of MESI. Moreover, tests performed at 30 °C, 40 °C and 50 °C showed that MESI can also delay the cement hydration at higher temperatures. The influence of potassium methylsiliconate on the compressive strength of cement mortar and concrete after 1, 2, 7, 28 days and72 days was also investigated. In the first days of hydration, the compressive strength of the materials was reduced, but after 28 days of curing the compressive strength was increased by 21% and 16% for cement mortar and concrete, respectively. The impact of MESI on the microstructure and pore size distribution of cement pastes in 2nd, 7th and 28th of hydration was examined by mercury intrusion porosimetry (MIP). The result showed significant delay in the development of the cement pastes microstructure during the first days of hydration. The XRD and DTA/TG analysis provided the knowledge about impact of siliconate on the composition and formation of the cement phases. Both, the XRD and DTGA/TG analyze showed noticeable changes in portlandite formation during the first days of hydration. The conducted research and obtained results reveal the innovative and novel application of potassium methylsiliconate as retarders, which prolongs the workability of fresh mixture and improves the compressive strength of matured concrete and mortar. This admixtures can be a competitive alternative to traditional retarders.

Tartaric acid effects on hydration development and physico-mechanical properties of blended calcium sulphoaluminate cements

The fast setting of calcium sulphoaluminate (CSA) cement-based systems is typically controlled using set-retarding admixtures, despite the notable efficiency of tartaric acid (TA) in adjusting CSA-based mixtures setting times, its use has only been marginally investigated, with an almost exclusive focus on the early age properties of TA manufactured mortars. This paper aims at evaluating the effect of the addition of tartaric-acid retarder on the hydration mechanism and physical properties of CSA-based mixtures from 4 h to 84 days. Macro- and microstructural properties were investigated using X-ray diffraction and differential thermal-thermogravimetric analyses, mercury intrusion porosimetry measurements, mechanical tests and analyses at fresh and hardened state. The experimental results reveal that the use of TA delays the formation of ettringite, modifies the porosity of hardened mixtures and strongly reduces strength in the short term. Nevertheless, the addition of TA slightly influences the properties at longer periods.

Alkali-activated natural pozzolan/slag binders: limitations and remediation

To address issues related to fast setting time of high-calcium-based alkali-activated binders and low-calcium-based alkali-activated binders' need for curing at elevated temperatures, this study aimed to develop hybrid low-calcium- and high-calcium-based binders with satisfactory fresh and hardened properties. This study was divided into two main phases: (i) production of alkali-activated natural pozzolan/slag pastes that can provide similar properties – particularly setting time – to those of Portland cement paste; (ii) confirmation of the pastes’ performance through their application in mortar and concrete mixtures. Different strategies including using various set-retarding admixtures, reducing the sodium hydroxide concentration and varying the combination of alkaline activators were considered to achieve this objective. The use of different chemical admixtures including commercial retarders, malic acid, sodium phosphate, phosphoric acid, sodium gluconate, a lignosulfonate-based admixture and gypsum, as well as a varying combination of alkaline activators, rendered fruitless to produce alkali-activated natural pozzolan/slag binders with acceptable setting time, flowability and strength. Optimising sodium hydroxide concentration was found to be the most effective method for achieving the expected performance of natural pozzolan/slag binders activated with sodium hydroxide and sodium silicate. The performance of mortars and concretes made with the resulting alkali-activated natural pozzolan/slag binders was promising. They achieved similar fresh properties and strength and had superior transport and durability properties to those of reference Portland cement mixtures.

Effect of Re-vibration on Strength Properties of Lightweight Concrete

Abstract In relatively deep structural members, re-vibration is applied to sequential layers after they are initially hardened. This may cause harmful effects on strength properties, especially on lightweight concrete (LWC). In this experimental study, the effects of re-vibration on LWC properties were thoroughly investigated. Local lightweight crushed pumice rock named “Bonza,” as well as set retarding admixture and silica fume (SF) were used to produce four different mixes of LWC. These mixes were re-vibrated at different time lags (0:00, 2:50, 4:30, and 5:30 [h:min]). After the re-vibration process, compressive and tensile strength properties, as well as pulse velocity, density, and permeable voids volume of hardened concrete mixes, were investigated. Results showed that using the setting retarder and partial SF replacement of Portland cement, the density, compressive, and tensile strength properties were increased in all re-vibrated mixes when the re-vibration was accomplished before the final set time of the cement. A lack of correlation between ultrasonic pulse velocity, density, and compressive strength was also detected. Furthermore, a linear relationship was found between permeable voids volume and compressive strength of all mixtures.

CSA-based Portland-free binders to manufacture sustainable concretes for jointless slabs on ground

The paper is aimed to the evaluation of the influence of water/binder ratio, tartaric acid dosage and curing condition on rheological, elastic and physical properties of sustainable shrinkage-compensating concretes manufactured with calcium sulphoaluminate cement (CSA), anhydrite (CS¯) and supplementary cementitious materials (SCMs)/lime (CH) compound in place of ordinary Portland cement (OPC). Results indicated that tartaric acid-based set-retarding admixture governs the behavior of concrete both in fresh and hardened state. In addition, according to Abram’s model, results evidenced the water/binder ratio as a key factor in strength gain. Moreover, tartaric acid allows the production of shrinkage-compensating Portland-free concretes particularly indicated for slabs on ground. Finally, by replacing OPC with SCMs and lime, it is possible to obtain, both for CO2-emissions and energy consumption, a reduction up to 60% at equal strength class respect to an OPC-based concrete.

Use of tartaric acid for the production of sustainable Portland-free CSA-based mortars

The purpose of the study is to evaluate the effect of a tartaric acid-based set retarding admixture on rheological, elastic and physical performances of sustainable mortars manufactured with calcium sulfoaluminate, anhydrite and Supplementary Cementitious Materials replacing totally OPC. Experimental results indicated that the tartaric acid acts as superplasticizer and it is effective to extend the pot-life of mortars up to about 2 h. On the other hand, the set-retarding admixture provides a strong retardation of binder hydration resulting in a reduction of initial expansion and compressive strength at early ages. However, this retarding effect disappears at long ages.

Influence of set retarding admixtures on calcium sulfoaluminate cement hydration and property development

Little published data is available to guide specification calcium sulfoaluminate cement (CSA) mixtures with citric acid retarder dosage rates capable of achieving adequate field working times, nor to understand the effect of retarder dosage on hydration and property development, representing a significant barrier to widespread CSA concrete use. Thus, this study investigated the use of citric acid with two commercially-available CSA cements, tracking the effects of dosage on phase development, hydration, setting, and compressive strengths. Key findings were that: citric acid successfully retarded initial set past 120min for both cements despite significantly different chemistries; increasing cement anhydrite content reduced retarder effectiveness and altered hardened binder microstructure, reducing compressive strengths; greater retarder dosages did not negatively affect cumulative hydration, nor strengths; and the time at which the maximum rate of heat evolution occurred correlated with final setting, a relationship useful for predicting field mixture behavior based on laboratory testing.

INFLUENCE OF SILICA COLLOID ON RHEOLOGY OF CEMENT PASTE WITH SUPERPLASTICIZER

Information of rheological behavior of binder paste is important for proportioning high slump concrete mixture at low water to cement ratios. This paper presents experimental data on the rheological property of silica colloid incorporated binder paste using naphthalene based and polycarboxylate based superplasticizer, compared to that of silica fume incorporated binder paste. Experimental data showed that silica colloid incorporated binder is compatible to tested superplasticizers in the all investigated range of silica colloid content, whereas the pastes incorporated with high silica fume content (over 10%) indicated incompatibility, especially to naphthalene based superplasticizer. There was also found out saturated content of superplasticizer corresponding to every kind of binder and water-binder ratio, with and without set retarding admixture.

Magnesium phosphate cement formulated with low grade magnesium oxide with controlled porosity and low thermal conductivity as a function of admixture

Magnesium phosphate cement (MPC) formulated with low-grade magnesium oxide (LG-MgO) can be better considered as sustainable MPC (sust-MPC). Among other properties, sust-MPC could be used as building material for constructive elements because of its acoustic and thermal insulation properties. Porosity and thermal conductivity are two important parameters that have a significant influence on thermal insulation properties. In this regard, this work aimed to obtain a highly porous sust-MPC with enhanced properties for thermal insulation. To this end the percentage of porosity as a function of both the amount of set-retarding admixture and the kneading water needed was assessed using a statistical design of experiments (DoE) approach. Additionally, thermal conductivity was also evaluated with respect these two factors. Last but not least, an optimized dosage was sought in order to maximize the percentage of porosity while achieving the lowest thermal conductivity. According to the results obtained, the statistical method successfully predicted the effects of variables on the final properties. Hence, a model that explains the overall behavior of the system was successfully attained. The obtained model predicts the porosity and the thermal conductivity of sust-MPC by means of the mixture dosage. Consequently, the present work demonstrates that it is possible to control the porosity in order to diminish thermal conductivity.

Chemical admixtures dose optimization in pervious concrete paste selection – A statistical approach

Making good-quality portland cement pervious concrete (PCPC) requires utilization of chemical admixtures. Several types of admixtures, including superplasticizers (SPs), viscosity modifying admixtures (VMA), and set-retarding admixtures (RE) are commonly used in PCPC. These chemical admixtures significantly influence the flowability, film-forming ability and film-drying time (setting time) of the paste component. Consequently, the workability of the PCPC mixtures is greatly affected by the type and amount of chemical admixture added. This paper shows how the Box–Behnken (BBD) response surface design can be used to characterize the individual and combined effects of SP, VMA and RE on pervious concrete paste. The paste properties evaluated include flowability, film-forming ability and film-drying time. Using the BBD technique, ranges of admixture combinations were studied with a reasonable amount of data points. Finally, mathematical equations (models) and response surfaces were developed. The models and the response surfaces could be used to select admixture doses for different type of PCPC mixtures. Therefore, this method is highly recommended for situations where concrete producers are required to create PCPC mixtures, which have variable mixture composition and material properties.

Effects of chemical admixtures and curing conditions on some properties of alkali-activated cementless slag mixtures

This paper reports the results of an investigation on the influences of admixtures and curing conditions on some properties of Alkali-Activated Slag (AAS) mixtures with no cement. In the study, Shrinkage-Reducing (SRA) and superplasticizing and setretarding (WRRe) admixtures were used. For the slag activation, sodium metasilicate was used at two sodium concentrations, 4% and 6% by mass of slag. Setting time, flow loss of fresh mixtures, and shrinkage strain, carbonation, flexural and compressive strength of hardened mixtures were measured. The test results showed that the admixtures generally had no impact on the setting times of AAS pastes. WRRe increased the flow rate of AAS mortars while SRA partially affected the flow values of AAS mortars. WRRe and SRA did not produce an important difference on the carbonation depths of AAS mortars. However, WRRe and especially SRA admixtures decreased the shrinkage values of AAS mortars. Additionally, curing conditions had a significant effect on the mechanical behavior in the hardened state of AAS mortars compared to Normal Portland Cement (NPC) mortars, and the strength development of AAS mortars at early ages was very fast in comparison with NPC mortars when subjected to elevated temperature.

Use of calorimetry and other methods in the studies of water reducers and set retarders interaction with hydrating cement paste

The calorimetric method was used as a main tool in the studies of the effect of superplasticizing and set retarding admixtures on cement hydration. The experiments were carried out using two types of cements (neat Portland cement CEM I 42.5R and blended Portland cement type CEM II/B-M (S-V) 42.5N), at varying w/c ratio 0.5 and 0.3 respectively. The hampering of cement hydration process at early age in the presence of these admixtures was generally observed. This is in practice equivalent to the set retardation. The dissolution, as well as the precipitation of hydration products were retarded too, as it has been proved by the DTA/TG, conductometric measurements and the evaluation of so-called chemical shrinkage. However in case of superplasticizers, after a prolonged “dormant” period the process is continued; the reactions occur at fairly good rate giving substantial heat effects – it can be concluded from the total heat evolved values after standard 41h. At longer time a significant amounts of products are formed as well, but it seems that the crystallization of calcium oxide is disturbed; simultaneously the amount and composition of calcium silicate hydrates alters towards the “more amorphous” product. This could be observed under SEM. The set retarders give strong delaying effect, particularly at low amount of water and in the pastes produced from Portland cement. This can be due to the formation of insoluble layer of calcium and sugar or calcium and phosphorus containing compounds surrounding the hydrating grains; the formation of this “barrier” can be distinguished as a small peak on the calorimetric curve and it is poorly removable on further hydration. The shrinkage and conductivity measurements seem to prove not only the change of kinetics of heat evolution/hydration but also the modification of the process and resulting products.

Influence of admixtures on the properties of alkali-activated slag mortars subjected to different curing conditions

This paper presents the influence of shrinkage-reducing (SHR) and superplasticizing and set-retarding admixtures (SSRe) on the properties of slag pastes and mortars activated by liquid sodium silicate with different dosage and modulus ratio. Properties in the fresh and hardened state for these binders were investigated by means of measuring some properties including setting time, flowability, flexural strength, compressive strength, carbonation and shrinkage. In this study, fifteen pastes and mortars were prepared. Liquid sodium silicate was used to activate the slag at two sodium concentrations, 4% and 6% by mass of slag. Liquid sodium silicate and sodium hydroxide were blended to obtain 0.75 and 1 modulus ratio of SiO2/Na2O. Results showed that although the higher percentage of sodium in the activator produced a higher strength, workability and setting times rapidly decreased with the higher sodium concentration due to instantaneous reaction and quick hardening of slag activated by liquid sodium silicate. None of the admixtures generally had an impact on the setting times of alkali-activated slag (AAS) pastes. SSRe admixture increased the flow rate of AAS mortars while SHR admixture partially affected the flow values of AAS mortars. SHR admixture exhibited a slight decrease in the carbonation depths of AAS mortars. SSRe and particularly SHR chemical admixtures reduced the shrinkage of AAS mortars. However, the shrinkage values of AAS mortars still were higher than those of ordinary Portland cement (NPC) mortars. Curing conditions had a significant effect on the mechanical behavior in the hardened state of AAS mortars compared to NPC mortars.

The Potentials of Cassava Flour as a Set-Retarding Admixture in Concrete

The potentials of cassava flour as a set-retarding admixture in concrete were investigated. Concrete mix proportion of 1:2:4 by weight of cement, sand and coarse aggregate and, water/cement ratio of 0.46 was made with six different dosage levels of cassava flour as admixture. The properties tested include setting time, workability of the fresh concrete and compressive strength of the hardened concrete. These properties were compared with those of similar concrete mix made without cassava flour admixture. It was observed that cassava flour considerably improved the workability of the fresh concrete and delayed the setting time of cement by up to 6 hours. Results of the tests also show that while cassava flour reduced the early strength of concrete, the long-term strength was improved. Cassava flour dosage level of 3% was also found to be the optimum level of addition of the admixture.

Using the Maturity Method in Concrete Produced with Setting Agents

The maturity function provides a reliable approach in the determination of the in situ strength of concrete at later ages. This study was aimed at determining the strength — maturity relationship on concrete specimens which were prepared using different admixtures and cured under different temperatures. For this reason, three sets of concrete specimens, having dimensions of 15×15×15 cm, were produced using the set accelerating admixture, set retarding admixture, and no admixture content at a constant consistency and 0.59 water-to-cement ratio. All hardened concrete specimens were cured at 0, 20, and 40°C temperatures under 100% humidity for 1, 3, 7, and 28 days. The compression tests were applied on specimens at the end of the curing time. Equations for the relationship between maturity and strength were worked out for the admixtures used in the study.

Simple Field Tests to Characterize Fluidity and Washout Resistance of Structural Cement Grout

Abstract The ability to assess rheological properties of neat cement grout, such as those used in structural repair and for filling post-tension ducts, is of special interest for the evaluation of the ease of pumping, spreading into place, and filling of narrow spaces. There is an increasing need to identify dependable and simple test methods that can characterize the consistency of specialty cement grouts and reflect variations in rheological properties during handling and placement. Several tests can be used to evaluate the rheological characteristics of a cement grout suspension, including precise methods for the determination of rheological parameters and simple procedures to assess fluidity. Rheological properties can be accurately determined by using a coaxial cylinder viscometer. However, the use of such a viscometer is mainly limited to the laboratory, and simple methods including the mini-slump spread and the modified Marsh cone tests are usually employed in the field to verify the consistency for quality control. This paper attempts to establish relationships between rheological parameters and fluidity values obtained using simple test methods. Relationships are also determined between the wash-out resistance of structural cement grout and various fluidity and rheological parameters. The derived relationships are based on a wide variety of cement grouts covering up to 210 data points. The various grouts were prepared with W/C ranging between 0.30 and 0.50, Type I and III portland cements, as well as various silica fume replacement values (up to 8% by mass), blast-furnace slag contents of 20 to 60%, fly ash substitutions of 10 to 30%, and limestone filler replacements of up to 30%. The investigated grouts incorporated melamine- and naphthalene-based high-range water reducer, welan gum and cellulose-based viscosity-modifying admixtures, as well as set-retarding admixture. Test results highlight the difficulties of relying on a single empirical test to evaluate the fluidity of a given grout. Correlations between various simple measurements of fluidity and wash-out mass loss and apparent viscosities determined at different shear rates indicate that the mini-slump and wash-out mass loss measurements correspond well to viscosities determined at low-shear rates (5.1 s-1). In contrast, the modified Marsh cone measurement corresponds well to viscosity determined at high-shear rates ranging between 340 and 510 s-1. Because of the pseudo-plastic behavior of structural cement grouts, field quality control tests should include fluidity assessment at low and high shear rates to adequately evaluate the rheological behavior of the grouts.

Use of Surface-Active Agents in Construction Industry

Surface-active agents as chemical admixtures are widely used in concrete industry to improve the properties of fresh concrete. By the introduction of admixtures, the use of high strength concrete with low water content became popular, and the durability of concrete structures was largely improved. The most frequently used admixtures are (1) water-reducing and setretarding admixtures to reduce the water requirement of concrete or retard the set, or both [these include ligninsulfonic acid, hydroxylcarboxylic acids, carbohydrates, polyols, and the salts], (2)air-entraining admixtures to introduce a system of small air bubbles into the fresh concrete dung mixing [these are anionic surface-active agnets]. A new group of water-reducing admixtures, termed superplasticizers, has been introduced in the last few years [these are naphthalenesulfonic acid, specific ligninsulfonic acid, and polycarboxylic acid]. They are about twice as effective as the conventional admixtures.

A Study on the Reuse of Plastic Concrete Using Extended Set-Retarding Admixtures.

The disposal of ready mixed concrete truck wash water and returned plastic concrete is a growing concern for the ready mixed concrete industry. Recently, extended set-retarding admixtures, or stabilizers, which slow or stop the hydration of portland cement have been introduced to the market. Treating truck wash-water or returned plastic concrete with stabilizing admixtures delays its setting and hardening, thereby facilitating the incorporation of these typically wasted materials in subsequent concrete batches. In a statistically designed experiment, the properties of blended concrete containing stabilized plastic concrete were evaluated. The variables in the study included (1) concrete age when stabilized, (2) stabilizer dosage, (3) holding period of the treated (stabilized) concrete prior to blending with fresh ingredients, and (4) amount of treated concrete in the blended batch. The setting time, strength, and drying shrinkage of the blended concretes were evaluated.For the conditions tested, batching 5 % treated concrete with fresh material did not have a significant effect on the setting time, strength, or drying shrinkage of the resulting blended concrete. Batching 50 % treated concrete with fresh materials had a significant effect on the setting characteristics of the blended cocnrete, which in turn affected the water demand to maintain slump. The data suggests that for a known set of conditions, the stabilizer dosage can be optimized within a relatively narrow range to produce desired setting characteristics. The strength and drying shrinkage of the blended concretes were essentially a function of the water content at different sampling ages and the relationship followed the general trend of control concrete.

Influence of set-retarding superplasticisers and microsilica on setting times of pastes at various temperatures

The influence on setting times of pastes made with microsilica and set-retarding superplasticisers at various ambient temperatures was investigated. Nine different pastes were designed to demonstrate the sole effect of different levels of microsilica and the combined effect of microsilica and set retarding superplasticisers at four temperatures; 20°, 30°, 40°, and 5 0 dot C. The results indicated that the inclusion of microsilica reduces consistency and retards setting at all temperatures. The set-retarding admixture was capable of retarding setting at 20°C but its efficiency was significantly hindered by the high ambient temperatures.