SCC mixes with poorly graded aggregate and high volume of limestone filler

Nonpozzolanic fillers are frequently used to optimise the particle packing and flow behaviour of cementitious paste in self-compacting concrete (SCC) mixes. This paper deals with the influence of finely ground limestone and crushed limestone dust on the properties of SCC mixes in the fresh and hardened state. Mixes were prepared using poorly graded crushed limestone aggregate. To compensate the lack of fine material in the crushed sand, a viscosity agent (VA) was added to the mixtures. The results obtained indicate that finer and better-graded limestone dust significantly increases the deformability of the paste. When a high volume of this filler was added to the SCC mix, the required self-compacting properties were achieved at a lower water/(cement+filler) ratio, and it also appeared that the addition of filler improves the 28-day compressive strength of concrete mixes due to the filler effect and improved fine-particle packing.     

A study on the applicability of vibration in fresh high fluidity concrete

The introduction of superplasticizers (Sp) in the production of concrete has produced highly flowable mixtures with enhanced viscosity. In cases of optimum flowability and viscosity, for example self-compacting concrete (SCC), no vibration is necessary for placement. However, such ideal conditions are not practically easy to achieve and deviations are possible. This paper reviews the results of a study to investigate the vibration of such high fluidity concrete. Two criteria were used to characterize the fresh mix, that is, slump flow and V-funnel time (V-time). Firstly, the feasibility of vibration on such mixes was studied. Then, the significance of flowability and viscosity was determined. Next, the relationship between workability and its segregation tendency was investigated. Finally, concrete mixes that missed SCC criteria were vibrated. Three different scenarios of vibration were concluded: namely, mix that accept vibration freely, mix that required controlled vibration and mix that needed prior treatment of viscosity enhancing agent (VEA) before vibration.     

Medium strength self-compacting concrete containing fly ash: Modelling using factorial experimental plans

Fresh self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact, without any segregation and blocking. The elimination of the need for compaction leads to better quality concrete and substantial improvement of working conditions. SCC mixes generally have a much higher content of fine fillers, including cement, and produce excessively high compressive strength concrete, which narrows its field of application to special concrete only. To obtain maximum benefit from SCC, it has to be adopted in general concrete construction practice. Such practice requires inexpensive and medium strength concrete.This investigation aims to develop medium strength SCC (MS-SCC). The cost of materials will be decreased by reducing the cement content and by using pulverised fuel ash (PFA) with a minimum amount of superplasticizer (SP). A factorial design was carried out to mathematically model the influence of five key parameters on filling and passing abilities, segregation and compressive strength, which are important for the successful development of medium strength self-compacting concrete incorporating PFA. The parameters considered in the study were the contents of cement and PFA, water-to-powder (cement+PFA) ratio (W/P) and dosage of SP. The responses of the derived statistical models are slump flow, fluidity loss, Orimet time, V-funnel time, L-box, JRing combined to the Orimet, JRing combined to cone, rheological parameters, segregation and compressive strength at 7, 28 and 90 days. Twenty-one mixes were prepared to derive the statistical models, and five were used for the verification and the accuracy of the developed models. The models are valid for mixes made with 0.38 to 0.72 W/P, 60 to 216 kg/m³ of cement content, 183 to 317 kg/m³ of PFA and 0% to 1% of SP, by mass of powder. The influences of W/P, cement and PFA contents, and the dosage of SP were characterised and analysed using polynomial regression, which can identify the primary factors and their interactions on the measured properties. The results show tha MS-SCC can be achieved with a 28-day compressive strength of 30 to 35 MPa by using up to 210 kg/m³ of PFA.     

Properties of fresh and hardened concrete

The present paper reviews the literature related to the properties of fresh and hardened concrete published after the previous (12th) International Congress on the Chemistry of Cement held in Montreal in 2007.Workability and fundamental rheological properties, reversible and non-reversible evolution, thixotropy, slump loss, setting time, bleeding, segregation and practical issues related to formwork filling and pressure, are addressed among the properties of fresh concrete.Among hardened concrete properties compressive strength and other mechanical and physical properties of hardened concrete, such as tensile strength, elastic properties, shrinkage, creep, cracking resistance, electrical, thermal, transport and other properties are covered. Testing, interpretation, modeling and prediction of properties are addressed, as well as correlation with properties of fresh concrete and durability, effects of special binders, recycled and natural aggregates, fiber reinforcement, mineral and chemical admixtures. Special attention is given to the properties of hardened lightweight and self-compacting concrete.     

Effects of experimental ternary cements on fresh and hardened properties of self-compacting concretes

Self-compacting concrete (SCC) is a concrete that flows alone under its dead weight and consolidates itself without any additional compaction and without segregation. As an integral part of a SCC, self-compacting mortars (SCMs) may serve as a basis for the mix design of concrete since the measurement of the rheological and viscosity properties of SCC is often impractical due to the need for complex equipment. This paper discusses the properties of SCM and SCC with mineral additions. ordinary Portland cement (OPC), natural pozzolana (PZ), and marble powder (MP) are used in ternary cementitious blends system following the cement substitution with PZ and MP in ratio 1/3. Within the framework of this experimental study, a total of 12 SCM and 6 SCC were prepared having a constant w/b ratio of 0.40. The fresh properties of the SCM were tested for mini-slump flow diameter, mini-V-funnel flow time, and viscosity measurement. Slumps flow test, L-box, J-ring, V-funnel flow time, and sieve stability were measured for SCC. Moreover, the development in the compressive strength was determined at 3, 7, 28, 56, and 90 days. Test results have shown that using ternary blends improved the fresh properties of the mixtures. The combination of natural pozzolana and marble powder increase the slump flow test up to 826 mm for the mixture prepared with 10% of mineral additions. Moreover, the use of mineral addition reduced the time flow to 4.27 s for SCC with 20% mineral addition, thus reducing the viscosity of all mixtures. Addition of MP increases the capacity of the passage through the plates between 88.75 and 93.50% for SCC with 7.5 and 15% of MP, respectively. The ternary system (PZ and MP) improve the sieve stability with the value for 4.07% of SCC with 50% of substitution compared for SSC without additions. The compressive strength of SCC at 90 days with 40% of PZ and MP was similar to that of OPC.     

Self-consolidating concrete incorporating new viscosity modifying admixtures

Self-consolidating concrete (SCC) is known for its excellent deformability, high resistance to segregation and use without applying vibration in congested reinforced concrete structures characterized by difficult casting conditions. The use of viscosity modifying admixtures (VMA) has proved very effective in stabilizing the rheology of SCC. Commercial VMAs currently available on the market are costly, which increases the cost of such a concrete. This article presents the suitability of four different types of new polysaccharide-based VMA in the development of SCC. A preliminary investigation was carried out on the rheological properties and setting times of mortar mixes with various types and dosages of VMA to study the influence and suitability of new VMAs. A more detailed study was then carried out on the SCC fresh and hardened properties such as slump flow, segregation, bleeding, flow time, setting time and compressive strength of different mixes with various dosages of an identified new VMA. The performance of various SCC mixtures with the new VMA was compared with a SCC using a commercial VMA designated as “COM” and a SCC mixture with Welan gum. The study on new VMA is encouraging and confirms the production of satisfactory SCC with acceptable fresh and hardened properties comparable with or even better than that made with commercial VMA and Welan gum. The suggested mix with 0.05% of the new Type A VMA satisfies the requirement of fresh and hardened properties of SCC and will require 7% less VMA dosage than that required in the commercial VMA mixture. The SCC with new VMA is also cost-effective.     

The effect of measuring procedure on the apparent rheological properties of self-compacting concrete

Torque versus time during testing of the rheological properties of fresh concrete has been investigated. The testing was performed in a BML viscometer and on a self-compacting concrete (w/c=0.45, 70% rapid hardening Portland cement, 3% silica fume, 27% fly ash, third generation superplasticizer). The relaxation period needed to obtain steady-state flow may affect the rheological properties estimated and should be taken into account in the selection of measuring procedures. Nonsteady state is likely to cause an overestimation of the plastic viscosity and an underestimation of the yield value. Furthermore, lack of steady state may explain the apparent shear-thickening behaviour of self-compacting concrete reported elsewhere.     

Effects of marble powder as a partial replacement of cement on some engineering properties of self-compacting concrete

Self-compacting concretes (SCC) are highly fluid concretes that can flow and be placed in formwork under their own weight without the requirement of internal or external energy. This fluidity is obtained with the use of high paste volume and superplasticizer. The paste of SCC is made principally of cement, which is the most expensive component of concrete. As a result, the production cost of SCC is higher than conventional concrete. However, to make the manufacture of SCC more practical and economical, the binder is often a binary, ternary even quaternary compound: Portland cement mixed with mineral additions. The primary aim of this work is to study the effect of incorporating the marble powder as a supplementary cementations material on the rheological and mechanical properties of SCC. The fresh properties were measured using the slump flow, J-Ring, V-funnel, and modified slump flow. The properties of hardened SCC such as strengths and ultrasonic pulse velocity (UPV) were determined at age of 3, 28, and 90 days. The results have shown that using of marble powder in SCC enhances their fresh properties. At hardened state, the incorporation of marble powder decreases the mechanical strengths and UPV. It can be noted that it is possible to produce an economical SCC when the cement is partially substituted by the marble powder.     

The use of quarry dust for SCC applications

Limestone powder has been the traditional material used in controlling the segregation potential and deformability of fresh self-compacting concrete (SCC). This paper deals with the utilisation of alternative materials, such as quarry dust, for SCC applications. Results from rheological measurements on pastes and concrete mixes incorporating limestone or quarry dust were compared. It was found that the quarry dust, as supplied, could be used successfully in the production of SCC. However, due to its shape and particle size distribution, mixes with quarry dust required a higher dosage of superplasticiser to achieve similar flow properties.     

Characteristics of a thermally activated alumino-silicate pozzolanic material and its use in concrete

This paper presents the results of the physical and chemical properties of a thermally activated alumino-silicate material (MK), and deals with the properties of fresh and hardened concrete incorporating this material. The properties of fresh concrete investigated included workability, bleeding, setting time, and autogenous temperature rise. The properties of the hardened concrete investigated included compressive, splitting-tensile and flexural strengths, Young's modulus of elasticity, drying shrinkage, resistance to chloride-ion penetration, freezing and thawing, and saltscaling resistance. The properties of the MK concrete were also compared with those of the control portland cement concrete and the silica fume concrete.

The test results indicate that the MK material is highly pozzolanic and can be used as a supplementary cementing material to produce high-performance concrete. Although it requires a higher dosage of the superplasticizer and air-entraining admixture compared with that of the control concrete, the MK concrete can be produced with satisfactory slump, air content, and setting time. The concrete incorporating 10% MK had higher strength at all ages up to 180 days compared with the control concrete; in comparison with the silica fume concrete the MK concrete showed a faster strength development at early ages, but had lower strength after 28 days. At 28 days, the MK concrete had somewhat higher splitting-tensile and flexural strengths, Young's modulus of elasticity, and lower drying shrinkage compared with that of the control and the silica fume concretes. The resistance of the MK concrete to the chloride-ion penetration was significantly higher than that of the control concrete, but similar to that of the silica fume concrete. The MK concrete showed excellent performance in the freezing and thawing test. The performance of the MK concrete subjected to the de-icing salt scaling test was similar to that of the silica fume concrete, but marginally inferior to the control concrete.     

Effect of limestone filler BET(H2O)-area on the fresh and hardened properties of self-compacting concrete

This paper presents a study on the use of limestone fillers with different specific surface area and their effect on the fresh and hardened properties of self-compacting concrete (SCC). The surface area was determined by a simplified BET method using water vapour as adsorbate. A rheometer and a slump flow test were used to measure the flowability of fresh concrete. A concrete dilatometer was used to measure the autogenous shrinkage, and a ring-test for the plastic cracking tendency. The compressive strength was determined at 28 days. It was found that the measure of BET(H₂O)-area can be used to evaluate the water requirement for constant workability of the SCC, where a change in BET(H₂O)-area of 1000 m²/kg corresponds to approximately 0.8% in moisture content. The results showed that filler with a large area will result in an increased autogenous shrinkage, decreased evaporation, lower plastic cracking tendency, and a higher compressive strength. With additional water the results was the opposite.     

Prediction of the plastic viscosity of self-compacting steel fibre reinforced concrete

Micromechanical constitutive models are used to predict the plastic viscosity of self-compacting steel fibre reinforced concrete (SCFRC) from the measured plastic viscosity of the paste. The concrete is regarded as a two-phase composite in which the solid phase is suspended in a viscous liquid phase. The liquid matrix phase consists of cement, water and any viscosity modifying agent (VMA) to which the solids (fine and coarse aggregates and fibres) are added in succession. The predictions are shown to correlate very well with available experimental data. Comments are made on the practical usefulness of the predicted plastic viscosity in simulating the flow of SCFRC.     

Effect of fine aggregate replacement with desert dune sand on fresh properties and strength of self-compacting mortars

This paper presents the results of an experimental study that investigated the rheological and mechanical properties of self-compacting mortars incorporating fine dune sand (DS), which has a tight Particle size distribution. Mortar mixtures were prepared with crushed sand (CS) or river sand (RS) in which the fine aggregates were replaced partially by different percentages of DS of 0, 25, 50, 75 and 100%. The effect of DS on the fresh mortars properties was studied using the mini-slump flow, V-funnel flow time and viscosity measurements tests. Compressive strength and flexural strength were determined at age of 3, 7 and 28 days. Experimental results indicate an improvement in fresh rheological without reducing in mechanical properties of self-compacting mortars when fine aggregates were replaced partially with DS (50%). However, at high-level DS replacement (75%) the slump flow decreases. The replacement of the DS to the CS or to the RS shows an increase in the mixture viscosity. In general, the compressive and flexural strength were not significant affected with an increase in DS replacement. Finally, based on the results obtained in this investigation, DS may provide a readily available alternative material as fine aggregates in mortar application.     

Properties of volcanic pumice based cement and lightweight concrete

The results of investigations on the suitability of using volcanic pumice (VP) as cement replacement material and as coarse aggregate in lightweight concrete production are reported. Tests were conducted on cement by replacing 0% to 25% of cement by weight and on concrete by replacing 0% to 100% of coarse aggregate by volume. The physical and chemical properties of VP are critically reviewed to evaluate the possible influence on both fresh and hardened state of cement and concrete. The standard tests on different Portland cement-volcanic pumice powder (VPP) mixes provided encouraging results and showed good potential of manufacturing Portland volcanic pumice cement (PVPC) with higher setting time using up to 15% of VPP. The properties of volcanic pumice concrete (VPC) using different percentages of volcanic pumice aggregate (VPA) were evaluated by conducting comprehensive series of tests on workability, strength, drying shrinkage, surface absorption and water permeability. It is concluded that the VPC has sufficient strength and adequate density to be accepted as structural lightweight concrete. However, compared to control concrete, the VPC has lower modulus of elasticity and has more permeability and initial surface absorption.     

Permeation properties of self-compacting concrete

Permeation properties, which include permeability, absorption, diffusivity etc., have been widely used to quantify durability characteristics of concrete. This paper presents an experimental study on permeation properties of a range of different self-compacting concrete (SCC) mixes in comparison with those of selected traditional vibrated reference (REF) concretes of the same strength grade. The SCC mixes with characteristic cube strength of 40 and 60 MPa were designed containing either additional powder as filler or containing no filler but using a viscosity agent. The results indicated that the SCC mixes had significantly lower oxygen permeability and sorptivity than the vibrated normal reference concretes of the same strength grades. The chloride diffusivity, however, appeared to be much dependent on the type of filler used; the SCC mixes containing no additional powder but using a viscosity agent were found to have considerably higher diffusivity than the reference mixes and the other SCCs.     

自密实橡胶混凝土性能研究综述

自密实橡胶混凝土是将废弃轮胎加工成橡胶颗粒并掺加到自密实混凝土中制成的新型建筑材料,相比于常规混凝土,其在硬化后具有脆性低、变形能力强、节能环保的显著优点。为了全面了解自密实橡胶混凝土的最新研究现状,从自密实性能(流动性、粘聚性、间隙通过性、抗离析性)、力学性能(抗压强度、劈裂抗拉强度、弹性模量、抗折强度、抗冲击性能、疲劳特性、阻尼比)、耐久性能(干收缩性能、吸水率、抗冻性、氯离子渗透性、电阻性)和内部微观结构等方面出发,对近十年间国内外针对自密实橡胶混凝土的研究进行了综合介绍。最后,归纳总结了研究结论,并为自密实橡胶混凝土的未来研究与推广提出若干建议。     

喷射3D打印磷酸镁水泥与混凝土界面粘结性能研究

本文结合喷射3D打印全角度智能建造与磷酸镁水泥(MPC)快硬早强、高粘结性能,研究喷射3D打印MPC与混凝土界面粘结性能。通过掺加偏高岭土(MK)和粉煤灰(FA)调控MPC凝结时间、流变和力学性能,研发可喷射3D打印MPC,分析喷射3D打印MPC与混凝土界面粘结强度和微观结构变化规律。结果表明:MK通过降低MPC水化放热速率可明显提高MPC凝结时间,FA可缩短MPC初凝与终凝时间差,进而提高喷射3D打印MPC稳定性;MPC抗折强度随MK掺量先增大后降低,FA可进一步提高MPC抗折强度;随MK掺量增加,MPC静态屈服应力逐渐提高,FA对MPC屈服应力作用不明显,但可显著降低MPC塑性粘度,当掺加30%MK和15%FA时,可保证MPC良好可喷射3D打印建造性和泵送性;喷射3D打印通过高速喷射挤压作用,提高MPC与混凝土界面以及MPC层间粘结强度,使喷射3D打印MPC层间及其与混凝土微观界面粘结密实。     

Tyre rubber waste recycling in self-compacting concrete

Rubberised self-compacting concrete was prepared containing different amounts of untreated tyre waste and their mechanical and microstructural behaviour are investigated and discussed in this paper. The fresh and hardened properties of such materials are compared with those of a typical reference formulation of self-compacting concrete. A comparison of the obtained compressive strengths with literature data confirms that self-compacting technology helps binding rubber phases.     

The effect of fly ash and limestone fillers on the viscosity and compressive strength of self-compacting repair mortars

Today, self-compacting mortars are preferred for repair purposes due to the application easiness and mechanical advantages. However, for self-compactability, the paste phase must meet some certain criteria at fresh state. The cement as well as the ingredients of the paste, powders with cementitious, pozzolanic or inert nature and plasticizing chemical admixtures should be carefully chosen in order to obtain a suitable paste composition to enrich the granular skeleton of the mix. The physical properties of powders (shape, surface morphology, fineness, particle size distribution, particle packing) and physico-chemical (time-dependent hydration reactions, zeta potentials) interactions between cement powder and plasticizer should be taken into consideration. All these parameters affect the performance of fresh paste in different manners. There is no universally accepted agreement on the effect of these factors due to the complexity of combined action; thus, it is hard to make a generalization.This study deals with the selection of amount and type of powders from the viewpoint of fresh state rheology and mechanical performance. The influence of powder materials on self-compactability, viscosity and strength were compared with a properly designed set of test methods (the mini-slump, V-funnel tests, viscosity measurements and compressive strength tests). It may be advised that, for each cement-powder-plasticizer mixture, a series of test methods can be used to determine the optimum content and type of materials for a specified workability.     

A new mix design concept for earth-moist concrete: A theoretical and experimental study

This paper addresses experiments on earth-moist concrete (EMC) based on the ideas of a new mix design concept. First, a brief introduction into particle packing and relevant packing theories is given. Based on packing theories for geometric packing, a new concept for the mix design of earth-moist concrete will be introduced and discussed in detail. Within the new mix design concept, the original grading line of Andreasen and Andersen [Andreasen, A.H.M. and Andersen, J., 1930, Ueber die Beziehungen zwischen Kornabstufungen und Zwischenraum in Produkten aus losen Körnern (mit einigen Experimenten). Kolloid-Zeitschrift 50, p. 217-228 (in German).], modified by Funk and Dinger [Funk, J.E. and Dinger, D.R., 1994, Predictive Process Control of Crowded Particulate Suspensions, Applied to Ceramic Manufacturing. Kluwer Academic Press, Boston.], will be used for the mix proportioning of the concrete mixtures.Mixes consisting of a blend of slag cement and Portland cement, gravel (4-16), granite (2-8), three types of sand (0-1, 0-2 and 0-4) and a polycarboxylic ether type superplasticizer are designed using the new mix design concept. The designed concrete mixes are tested in the lab, both in fresh and hardened states, to show the suitability of the ideas of the new mix design concept. The tested concrete mixes meet the requirements on the mechanical and durability properties.Furthermore, the application of fine stone waste materials in the form of premixed sand (Premix 0-4) is presented. By means of an optimized particle packing, stone waste materials can be used to reduce the amount of the most cost intensive materials in earth-moist concrete mixes, viz. binder and filler. The results of tests carried out on mortar samples as well as on paving blocks produced on a laboratory paving stone machine will be discussed. The application of fine stone waste materials in earth-moist concrete mixes does not only meet the current trends in raw materials use, but also fulfill the technical requirements of the concrete in fresh and hardened state.