Rate Of Slump Loss Research Articles

Development of Sustainable Slag-based Geopolymer Concrete Using Different Types of Chemical Admixtures

Geopolymer concrete (GPC) has achieved a wide popularity since innovating it as an alternative to conventional concrete because of its superior mechanical characteristics and durability, in addition to being a green concrete due to its low negative impact on the environment. However, GPC still suffers from the problem of its poor workability which suppresses its spread in construction applications. This study investigated the most effective parameters on the workability of GPC including GGBFS content, water to binder ratio, and dosage of different types of chemical admixtures, Naphthalene-Based Admixture (NPA) and Polycarboxylate-Based Admixture (PCA), using Taguchi approach and Analysis of Variance (ANOVA) analysis considering the compressive strength at the different concrete ages. It was observed that NPA, in the geopolymer concrete, improved the compressive strength compared to PCA. The NPA-based mixes achieved the highest 28-day compressive strength, 69 MPa, with about 27.8% more than the highest 28-day compressive strength achieved by the PCA-based mixes, 54 MPa. The obtained results revealed that the NPA has achieved the best improvement for both the workability, in terms of initial slump value and slump loss rate, and the compressive strength of GPC mixes compared to PCA.

Properties of slag geopolymer concrete modified with fly ash and silica fume

This research focused on the role of fly ash and silica fume on slag geopolymer concrete through investigating workability (slump, and slump loss), initial setting time, final setting time, and mechanical properties of slag geopolymer concrete (S-GPC) (compressive strength, splitting tensile strength, modulus of elasticity) in addition to scanning electron microscope (SEM) and X-ray analysis. The considered variables included fly ash content as a replacement of ground granulated blast furnace slag (GS) (0%, 10%, 20%, 30%, and 40%), presence of silica fume as a replacement for slag, concentration of sodium hydroxide, NaOH, (molarity: 10, 16, and 18 mol/L), additional water content (7.5%, 11%, 14%, and 20%), and curing type (thermal, air, and water curing). S-GPC yielded rapid stiffening and high slump loss with high mechanical properties. The use of silica fume or fly ash or a mix of both enhanced workability, decreased rate of slump loss, and delayed setting time. The ACI 318 equation overestimates splitting tensile strength of FS-GPC.

Effects of mixing water temperatures on properties of one-part alkali-activated slag paste

During hot and cold weather, initial mixing water temperature is a critical parameter in controlling the fresh and hardened properties of cement-based materials. With the advent of Alkali Activated Materials (AAMs), the effectiveness of such a technique becomes questionable as the hydration mechanism differs from that of the ordinary Portland cement (OPC). Therefore, this study focuses on evaluating the effects of initial mixing water temperature on the performance of one-part Alkali Activated Slag (AAS). Various AAS mixtures prepared by different mixing water temperatures (i.e. 0 °C, 10 °C, 20 °C, and 30 °C) were tested. Fresh and hardened properties, including mini-slump, slump loss rate, setting time, the heat of hydration, compressive strength, and shrinkage, were investigated. Results reveal that the initial mixing water temperature plays a dominant role in controlling solubility and dissolution rates for different ingredients (i.e. solid activator and slag). This, in turn, had affected the hydration process and consequently the development of various properties. Slump life and setting time were found to extend as the initial mixing water temperature reduced while the strength was not harmed. Saving energy consumed for warming water during cold weather concreting will also increase concrete sustainability. It is anticipated that these findings will pave the way for a broader implementation of such green sustainable materials in the construction sector.

The effect of mixing method on capillary moisture content of concretes with recycled concrete aggregates

Recycled concrete aggregate represents a major environmental burden in the affected area and its use as an aggregate in concrete production is widespread in many countries. However, such aggregates have worse characteristics and strength than those of natural aggregate. In particular they have a higher absorption rate than natural aggregates, need much more water for mixing, and cause a high slump loss rate depending on the elapsed time. In this context, it is possible to monitor globally extensive research aimed on the elimination of improper properties of alternative aggregates, which are an obstacle to their application in concrete. The sorptivity expressed by capillary moisture content is a characteristic of moisture transport into the material, and recently it has been recognized as an important performance characteristic of durability. The paper is focused on the specific approach to concrete mixing as a way of the improvement of recycled aggregate´s surface using 3 variations of powders as coating materials and 2 kinds of aggregate. The changes in the capillary moisture content are compared and discussed. It is clear that the kind of coating material can influence this performance parameter significantly, so the careful design of mixing process together with the selection of powdery materials is essential. The triple mixing method was found to be promising for recycled concrete aggregate concrete, when fly ash or recycled concrete powder are used in the first stage of mixing. It is a favourable result, taking into account the perspective of the application of secondary raw materials for concrete production.

A review of hot climate concreting, and the appropriate procedures for ordinary jobsites in developing countries

Hot weather concreting involves some procedures to reduce negative effects caused principally by excessive water evaporation from the concrete surface. Potential problems for fresh concrete are: increased demand for water, increased the tendency the rate of slump loss corresponding to add water on job-site, an increased in execution rate, increased tendency for plastic shrinkage cracking and increased difficulty in controlling occluded air. Potential problems for hardened concrete may include: reduction of resistance at 28 days and long-term resulting of higher water demand and/or higher temperature of concrete, decreased durability resulting from cracking. Most developing countries have hot climate, ordinary jobsites in developing countries are characterised by reduced of human resources, equipment and infrastructures. This paper briefly reviews hot climate concreting procedures, especially the latest research in developing countries, and discusses the most appropriate in developing countries.

Thermal effects of activators on the setting time and rate of workability loss of geopolymers

A number of parameters influence the properties of both fresh and harden geopolymer concretes. Similar to the case of OPC concretes, the fresh geopolymer concrete must also exhibit desirable rheology and setting behaviours in order to be useful for field applications. These properties of geopolymer concrete cannot be controlled using traditional super plasticisers, water reducer or set retarders. Therefore, the significance of understanding alternative methods to adjust the properties of fresh geopolymer concrete is very high.Use of solid alkali activators in geopolymer mixes is less hazardous than the commonly used liquid activators and yields a “cement like” mix, where only water is added for its activation and hydration. The alkali activators used in solid form instead of a liquid form changes the kinetics of the reaction, as its dissolution occurs during the mixing process. This paper presents a study of the setting time and rate of slump loss of geopolymer binders based on fly ash and slag blends and activated with pentahydrate and anhydrous sodium metasilicate. Fly ash and slag were mixed at different ratios and activated with the two solid alkali activators mentioned above. Vicat needle test and calorimetric measurements were employed to determine the setting parameters and heat generation and sink effect of geopolymer mixes. The workability was measured using a flow table to examine the rate of slump loss. The calorimetric measurements showed that activation of the fly ash and slag blend by the pentahydrate activator is accompanied by negative heat flow (heat absorption) whereas anhydrous alkali activator dissolution is accompanied by release of heat. The additional heat released during the dissolution process accelerates the setting in anhydrous alkali activated geopolymers compared to hydrated alkali activated geopolymers. It was also observed that the strength of the geopolymers in later stage changes with changing calorimetric heat flow characteristics.

USING OF INDUSTRIAL WASTE AS A GREEN CHEMICAL ADMIXTURE IN CONCRETE

In the modern construction practices, industrial wastes or by-products are largely used as raw materials in cement and concrete. It imparts positive environmental effect because the waste materials are not released to the environment; therefore, this research study was conducted to investigate the effects of used engine oil on properties of fresh and hardened concrete. The main variables included the type and dosage of admixture (commercially air entraining agent, used engine oil, and new engine oil), consistency, rate of slump loss, setting time and compressive and splitting tensile strength. Results showed that performance of used engine oil and the new engine oil mixes were similar. Results of this study also showed that used engine oil acted as a chemical plasticizer by improving the fluidity and the slump of the concrete mix. The used engine oil decreases the initial setting time and increases the consistency and rate of fluidity loss of ordinary Portland cement concrete. Effects of engine oil on the concrete compressive and splitting tensile strength were negative with respect to the control/reference mixes. However, engine oil concrete has a higher compressive and splitting tensile strength than the corresponding concrete mixes containing dosage of commercial air entraining agent.

Feasibility Study on Bisphenol A as Phenol Replacement to Produce Aminosulfonate-Phenol-Formaldehyde Superplasticizer for Application in Concrete

AbstractIn this study, phenol was replaced by a powdery bisphenol A to produce aminosulfonate -phenol-formaldehyde (ASPF) superplasticizer (SP); ASPF SP and aminosulfonate-bisphenol A- formaldehyde (ASBF) SP were prepared. ASPF and ASBF SPs have ─NH2, ─OH, ─CH2, ─C6H5, ─SO3 functional groups, the weight-average molecular weight of 17.22 and 18.61 kDa, respectively, and the average polydispersity index of 1.08 and 1.53, respectively. The cement particle surface with ASPF SP has a higher initial zeta potential than that with ASBF SP. Along with time, the zeta potential of the cement particle surface with ASPF and ASBF SPs of 10 g/L change from −15.42 and −15.30 mV, respectively, in initial time, to −15.62 and −15.72 mV, respectively, after 120 min. ASPF SP exhibits a higher water reduction percentage than ASBF SP. The concrete with ASPF SP has a higher slump loss rate and mechanical properties than that with ASBF SP. The air content, wet density, and setting times of cement pastes with ASPF and ASBF SPs ...

Effect of absorption of limestone aggregates on strength and slump loss of concrete

Abstract Slump loss of concrete is very important in construction practice particularly with ready-mixed concrete. It is believed that slump loss occurs due to reduction of mixing water caused by aggregate absorption, evaporation, and cement hydration. In this study, the effect of absorption of limestone aggregates on the effective w/c ratio and on the strength and slump loss of concrete was investigated. It was found that the absorption of dry aggregates in all concrete mixes considered in this study occurred mainly in the first 15 min after the start of mixing and diminished substantially thereafter. The rate of slump loss of concrete was almost identical for mixes with dry and wet aggregates, even when setting time was extended. The results indicated that limestone aggregates used in this study with an absorption capacity of 1.3–1.9% by weight can absorb about 75% of their absorption capacity when mixed in concrete. The remaining 25% will add to the free water, thus increasing the effective w/c ratio. This phenomenon was demonstrated by the increased initial slump and decreased compressive strength of mixes with dry aggregates compared to those with wet aggregates.

Impact of Extremely Hot Weather and Mixing Method on Changes in Properties of Ready Mixed Concrete during Delivery

Riyadh is located in central Saudi Arabia. Its extremely hot, dry environment was used to investigate concrete compressive strength, slump, and temperature changes during ready mixed concrete (RMC) delivery. Representing three plants employing a truck-mixing method and three plants employing a central-mixing method in their operations, testing was performed using a total of 80 delivery trucks. Differences in RMC property changes that were not significant were indicated by study results during delivery in both Riyadh's extremely hot, dry summertime environmental conditions and the midwestern United States' much milder summer conditions. The study showed that during summertime delivery, concrete slump lost 37% of its initial value and concrete temperature increased by an average of 1.1 degrees Celsius (2.0 degrees Fahrenheit). There was a slightly higher compressive strength at the site than at the plant. Long travel times did not significantly affect compressive strength. Effective control of adverse hot weather effects on concrete production and delivery, even under the region's extremely hot prevailing weather conditions, was shown possible by controlling concrete temperature, avoiding delivery during noon hours, and using water-reducing and retarding admixtures, per ACI 305R recommendations. In this study, there was no observation of the anticipated increased slump loss rate problem associated with hot weather use of water-reducing and retarding admixtures.

재생 골재 콘크리트의 슬럼프 손실 개선을 위한 분말형 감수제의 활용

In this study, powered superplasticizer(PSP) agents to improve the slump loss rate of recycled aggregate concrete were developed. To evaluate the variation of fluidity against elapsed time and the mechanical properties, twenty four specimens whose main variables had the mixing condition of aggregates, such as natural and recycled gravels, and natural and recycled fine aggregates, were tested. The concrete slump with a liquid superplasticizer greatly decreased against the elapsed time and dropped by less than 50% of initial slump after two hours. However the concrete slump with the PSP agents hardly varied until after half an hour and maintained more than 85% of initial slump even after an hour. Also the PSP agents made the compressive, splitting tensile, and flexural strength of concrete increased and the shrinkage strain decreased. Considering the properties improvement of concrete, it can be recommended that optimum mixing amount of the PSP agents should be 5% of the amount of cement.

Influence of dispersant structure and mixing speed on concrete slump retention

The relationship between rate of dispersant depletion from the aqueous phase and concrete slump retention was investigated by varying polycarboxylate dispersant structure and mixing speed. The influence of dispersant structure on the rate of slump loss was determined by testing two polycarboxylate-polyether dispersants that differed in charge density. The influence of mixing rate on slump loss was determined by changing mixer rotation speed. The rate of dispersant depletion was influenced by dispersant structure and mixing speed. A higher rate of dispersant depletion was observed at higher mixing speed and with a polymer of higher charge density. In comparing the different mixing procedures, a good correlation was found between slump value and the number of drum revolutions, while a poor correlation was found between slump value and time. Concrete slump retention was influenced by the rate of dispersant depletion and the rate of dispersant depletion was influenced by dispersant structure and mixing speed.

Evaluation of the performance of sulfonated esparto grass lignin as a plasticizer–water reducer for cement

The objective of the work described in this first paper of a series is an investigation of the preparation of a sulfonated esparto grass lignin (SEL) and its behavior as a plasticizing–water-reducing agent for cement–water systems. SEL is prepared by extracting the lignin from the black liquor of a soda esparto grass pulping process and then sulfonating it with a mixture of sodium sulfite and formaldehyde. Analyses and characterization of SEL carried out with high-performance size exclusion chromatography (HPSEC), reversed phase chromatography (RPC), infrared spectrometry and chemical methods show that both the molecular weight average and the combined sulfur content are relatively high. Moreover, HPSEC shows that SEL has a relatively more uniform molecular weight distribution (MWD) than the commercial products obtained from the sulfite wood pulping process. On the other hand, SEL could reduce the water content, improve the workability and compressive strength of mortars. SEL also permits a very low rate of slump loss of cements without excessive extension of the final set time.

Concrete design and construction from the inside out

The excitement of concrete design and construction is based in no small part on the broad range of options available for the color, shape, texture, architectural style, and structural systems available through use of this material concrete. But the excitement (and often the anxiety) that accompanies concrete construction is due to the rapid changes associated with concrete’s transition from a fluid-like, workable material that is similar to a saturated soil to its ultimate status as a brittle, artificial rock. The engines behind this transition are the hydration of the portland cement and reactions with other cementitious materials. While cement hydration is often considered to be of interest only to those in white lab coats, these chemical changes at microscopic level are played out in the “real world” in terms of the effects of mixing time, rate of slump loss, form pressures, time to start and end surface finishing, and the rate of increase of both strength and stiffness.

Hot weather concreting with admixtures

The adverse effects of elevated temperatures on the properties of the fresh concrete, namely increased water demand, shorter setting times and increased slump loss, are briefly discussed, and the possible use of chemical admixtures (ASTM C 494) to overcome these adverse effects, is examined in the light of present knowledge. The effect of water reducing and retarding admixtures (type D, ASTM C494) on plastic shrinkage and plastic shrinkage cracking, and the effect of fly ash class F (ASTM C 618) on slump loss, are also discussed. It is concluded that type D admixtures accelerate, rather than slow down the rate of slump loss in concrete subjected to prolonged mixing, but such admixtures are advantageous when used to reduce water demand and to delay setting times. Fly ash was found to reduce significantly the rate and amount of slump loss of concrete with and without admixtures. It is suggested, however, that under hot weather conditions, the combined use of class F fly ash and type D admixtures is to be recommended. Both retarders and fly ash were shown to increase the susceptibility of fresh concrete to plastic shrinkage cracking. Accordingly, when used, extra care should be taken to protect the fresh concrete from drying.

Slump loss and compressive strength of concrete made with WRR and HRWR admixtures and subjected to prolonged mixing

The effect of four water-reducing and retarding admixtures, and three superplasticizers on the consistency (slump) of fresh concrete, was studied at 21°C and 32°C in concrete mixes, made of OPC containing 10% fly ash, and subjected to prolonged mixing for up to 180 min. The effect of such mixing on compressive strength of concrete, at the ages of 3, 7, 28 and 90 days, was also studied. It was found that the admixtures in question accelerated the rate of slump loss at all ages, concrete compressive strength linearly increased with mixing time. The rate of slump loss, and the water demand of the concrete mixes increased within the temperature range studied.

High-Strength Semi-Lightweight Concrete with Up to 50% Fly Ash by Weight of Cement

Abstract This paper discusses the effects of including a Western Canadian subbituminous fly ash in superplasticized, air-entrained, semi-lightweight concrete. Mixtures were proportioned with 100 ± 20mm slump and 5 ± 1% air content. Cement contents ranged from 250 to 500 kg/m3 with additions of fly ash up to 50% by weight of cement. In the freshly mixed state, the effects of the fly ash are to reduce the initial water demand, increase the dosage of air-entraining admixture required for the specified air content, and reduce the rate of slump loss after addition of superplasticizer. The dosage of superplasticizer required remains essentially constant when expressed as a percentage of the total weight of binder (cement + fly ash). In the hardened state, the emphasis is on establishing how the proportion of fly ash to cement affects strength, unit weight, and cost. Each mixture is evaluated in terms of strength-weight ratio and cost in terms of cement equivalent in kg/m3, using the relationship between the costs of cement and fly ash locally to convert the cost of the fly ash into an equivalent cement cost. The bar chart used for this purpose readily facilitates the identification of optimal mixture proportions from the point of view of strength-weight ratio and cost. In addition, the development of strength is examined at various ages to show how the fly ash progressively asserts its effect on relationships between strength and effective W-C ratio. Finally, resistance to freezing and thawing is reported in terms of Procedure A of ASTM Test Method for Resistance of Concrete to Rapid Freezing and Thawing (C 666-84), and performance is shown to be unsatisfactory when using presaturated lightweight aggregate with the specified 14-day moist curing regime. Performance improves substantially after drying followed by further soaking simulative of the curing of lightweight concrete in structures following construction.

Retempering of plain and super plasticised concretes

This paper evaluates the use of water, superplasticiser and cement slurry as retempering agents for plain and superplasticised concretes. Water, the most economical retempering agent, produces significant loss in strength of concrete particularly for the superplasticised concrete. Cement slurry, although producing restoration of slump with no significant effect on strength, results in less workable concrete mix due to stickiness effect from the high cement content. Superplasticiser, despite its cost and influence of increasing the rate of slump loss, is the best retempering agent with any loss in strength.