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.     

Effects of local metakaolin addition on rheological and mechanical performance of self-compacting limestone cement concrete

Various mineral additions are used in the manufacture of self-compacting concrete (SCC) to reduce the cement content and hence the CO₂ emissions and also to enhance the performance of concrete. In this paper, the results of fresh and hardened properties of self-compacting limestone cement mortar (SCLCM) and concrete (SCLCC) with metakaolin (MK) as cement replacement are reported. SCLCM properties investigated include spread flow, V-funnel flow time, yield stress, plastic viscosity and heat evolution. SCLCC fresh properties include slump flow, V-funnel flow time, J-Ring, L-Box and sieve segregation. Compressive strength of the hardened SCLCC was measured at the ages of 1, 3, 7, 28, 90, and 180?days. Moreover, water porosity, water absorption by capillarity and dynamic modulus of elasticity (E_d) tests were conducted. Test results indicated that the produced MK is of sufficient pozzolanic activity and contributes to improve the performances of concrete in particular at later stages. The addition of MK to SCLCM mixes exhibits lower heat evolution, lower yield stress, higher plastic viscosity and higher V-funnel flow time. The addition of MK to SCLCC mixes improves the rheological properties (flowability, passing ability and segregation resistance) as well as the mechanical and durability performance.     

Rheological properties of cementitious materials containing mineral admixtures

The rheological properties of cementitious materials containing fine particles, such as mineral admixtures (MA), were investigated using a Rotovisco RT 20 rheometer (Haake) with a cylindrical spindle. The mineral admixtures were finely ground blast furnace slag, fly ash and silica fume. The cementitious materials were designed as one, two and three components systems by replacement of ordinary portland cement (OPC) with these mineral admixtures. The rheological properties of one-component system (OPC) were improved with increasing the dosage of PNS-based superplasticizer. For two-components systems, yield stress and plastic viscosity decreased with replacing OPC with blast furnace slag (BFS) and fly ash (FA). In the case of OPC-silica fume (SF) system, yield stress and plastic viscosity steeply increased with increasing SF. For three components systems, both OPC-BFS-SF and OPC-FA-SF systems, the rheological properties improved, compared with the sample with SF. In the two and three components systems, the rheological properties of samples containing BFS improved much more than with FA replacement alone.     

A study on the effect of fine mineral powders with distinct vitreous contents on the fluidity and rheological properties of concrete

This paper presents an investigation on the effects of fine mineral powders on the fluidity and rheological properties of concrete. It was observed that the fluidity of concrete increased noticeably, and the plastic viscosity decreased, when vitreous powders were substituted partially for cement. It was found that vitreous powders have a strong dispersion effect on the fluidity and rheological properties of concrete, and this effect can be correlated with the vitreous content of the powders incorporated.     

Estimating rheological properties of cement pastes using various rheological models for different test geometry, gap and surface friction

Shear stress-shear rate flow tests were carried out on various cement pastes incorporating different mineral additions and chemical admixtures using various test geometries. Different gaps and friction capacity of shearing surfaces of the test geometries were employed in the flow tests. Rheological properties of cement pastes were calculated from the resulting flow curves using various rheological models. The Bingham, Modified Bingham, Herchel-Bulkley and Casson models were used to estimate yield stress. Plastic viscosity was estimated by the Bingham, Modified Bingham and Casson models, while the Williamson and Sisko models were used to estimate the theoretical viscosity at zero and infinite shear rates. It was observed that the rheological properties of cement pastes varied with the change of the test geometries and rheological models used for their calculation. The performance of rheological models in estimating the rheological properties of cement pastes, as expressed by a standard error, varied with the test geometries as well as with the composition of cement pastes. The paper highlights the difficulty in reconciling rheological results from different sources and the need for standardizing rheological test methods for rheological interlaboratory results to be critically analyzed and compared.     

新拌石灰石粉-偏高岭土-水泥系统流变特性研究

石灰石粉和偏高岭土复掺可以替代部分水泥,有效降低水泥制品的碳排放。采用安东帕MCR 302旋转流变仪测试了新拌石灰石粉-偏高岭土-水泥浆体系统的流变特性。通过单纯形重心法对石灰石粉-偏高岭土-水泥砂浆系统进行了试验设计,利用Viscometer 5型混凝土流变仪对不同配比砂浆的流变特性进行了测试。结果表明：随着偏高岭土掺量的增加,水泥浆体的屈服应力和塑性黏度显著增大;随着石灰石粉掺量的增加,水泥浆体的屈服应力和塑性黏度呈先增大后减小的趋势;改变砂浆胶凝材料的配比能够显著影响砂浆的流动性以及流变参数。     

Yield stress and viscosity equations for mortars and self-consolidating concrete

The rheological behavior of flowable concrete, such as self consolidating concrete is closely influenced by concreting temperature and the elapsed time. The variation of the plastic viscosity and the yield stress with the elapsed time and temperature must be accurately quantified in order to forecast the variation of workability of cement-based materials. A convenient method to study the variation of these rheological parameters is proposed, using the mortar of the concrete. This latter is designed from the concrete mixture, taking in account the liquid and solid phases with a maximum granulometry of 315 μm. Different SCC and mortars proportioned with two types of high range water reducing admixtures (HRWRA) were prepared at temperatures ranging from 10 to 33 °C. Test results indicates that the yield stress and the plastic viscosity of the mortar mixtures vary in a linear way with the elapsed time while an exponential variation of these rheological parameter is seen on SCC. In order to enhance robotization of concrete, general equations to predict the variations of the yield stress and plastic viscosity with time are proposed, using the corresponding mortar initial yield stress and plastic viscosity. Such equations, derived from existing models, can easily be employed to develop concrete design software. Experimental constants which are related to the paste fluidity or the aggregates proportioning can be extracted from a database created with either mortar or aggregates test results.     

Formulation and rheology of eco-self-compacting concrete (Eco-SCC)

This article presents the results of an experimental study on the rheology of eco-SCC, formulated on the basis of the modified Chinese method and on the new standard EN206/CN. The studied ecological concretes consist of Portland pozzolana cement, containing large amounts of limestone filler or natural pozzolana, which can replace cement up to 50%. In addition, the compactness of the granular mixture is optimized; therefore, the total amount of the incorporated binder is further reduced in the body of concrete. The study of the rheological behavior of these fluid concretes was carried out in the laboratory, using a coaxial vane-type rheometer. The results showed that both rheological models, i.e. modified Bingham and Herschel–Bulkley, describe satisfactorily the shear-thinning character of the formulations tested. However, the rheological parameters obtained with the modified Bingham model seem to have better correlations with the measurements of the slump test. These same results also indicated that replacing 30% of cement by one of the additions selected for our study, resulted in mixtures with yield stress and plastic viscosities that are within the validity range of SCC. This allowed reducing CO₂ emissions by about 40% for each cubic meter of concrete produced.     

Prediction of fresh concrete flow behavior based on analytical model for mixture proportioning

Large number of experimental techniques and models has been developed recently in an attempt to link the parameters of Bingham equation to concrete composition. On the other hand, concrete mixture proportioning methods based on rheological approach usually do not provide direct input of a measurable rheological parameter(s) into the proportioning expression. In this study, series of concrete mixtures have been proportioned by the use of a theoretical model. The experimental results were compared with the predicted rheological quantity by the model. The evaluation of concrete flow parameters has been performed using a newly developed tube viscometer for concrete. The discussion presents a comparison between the model calculated apparent viscosity and the measured plastic viscosity of fresh mixes as function of volume fraction of solids, normalized with respect to their maximum packing values.     

硅微粉对水泥浆体流变性能的影响

运用水化热测定仪、流变仪、以及Dinger-Funk紧密堆积等方法,研究了硅微粉掺入水泥中对复合浆体的流变性能的影响,比较了不同硅微粉掺量对复合浆体的早期水化放热、紧密堆积程度、屈服应力和塑性粘度的作用.结果显示:硅微粉取代水泥后,降低浆体水化热放热量,提高了体系紧密堆积程度;Bingham流体仍适用于硅微粉-水泥复合浆体,取代5%、10%、15%水泥的复合浆体,屈服应力和塑性粘度在0、60 min时都小于纯水泥浆体,并且取代10%水泥的复合浆体,其屈服应力和塑性粘度在0、60 min时都最小,流变性能最好.     

Coupled effect of time and temperature on variations of plastic viscosity of highly flowable mortar

Self-consolidating concrete (SCC) is being increasingly used as construction material for its workability. However, the rheological properties of such concrete, which is made with significant concentration of high-range water-reducing admixture (HRWRA), depend in most cases on the casting temperature of the material. The study presented herein aimed at evaluating the coupled influence of time and temperature on the variations of plastic viscosity (µ) of micro mortar made with polymelamine (PMS), polynaphtalene (PNS) and polycarboxylate (PCP) polymer. In total, seven micro mortar mixtures proportioned with various binder compositions and water-to-binder ratios of 0.42 and 0.53 were prepared at 10 to 33 °C. Test results show that the plastic viscosity varies linearly with the coupled effect of time and temperature for mixtures made with PNS or PMS HRWRA. However, for mixtures made with PCP-HRWRA, both temperature and mixture proportioning have influence on the variation of viscosity with time.     

Effect of the type of superplasticizer on the properties of cementitious systems incorporating slag

Superplasticizers have become an integral ingredient in the formulation of concretes. After 40?years, their use and dosage remain uncertain due to variations in their compositions and those of cement. In addition, the substitution of cement by supplementary cementitious materials having different chemical compositions exacerbates the problem without counting the multiplicity of superplasticizers to choose from. The present work consists of a study of the rheological and mechanical properties of cementitious systems containing slag and various types of superplasticizers. The tests were carried out on pastes, mortars and concretes incorporating slag in partial cement replacement and four superplasticizers types, polynaphthalene sulphonate (PNS) and three polycarboxylates (PC). The results of this study demonstrate that the viscosity and the yield stress increase with the rate of incorporation of the slag. The air increases with the polycarboxylates but this effect is less perceptible in the presence of the slag. Polycarboxylates improve workability more than PNS. The use of polycarboxylates reduces the viscosity and the yield stress. The compressive strength of concretes containing slag is low at early age but high at long run. They exhibit good resistances to scaling. The permeability to chloride ions is considerably reduced in the presence of the slag independently of the type of superplasticizer, suggesting good durability of these concretes in potentially aggressive external environments.     

Effect of fly ash and nanosilica on compressive strength of concrete at early age

The replacement of cement by mineral admixtures in concrete has been of increasing interest in the construction industry. Nevertheless, several of the potential replacements, such as fly ash class F, lower the compressive strength of concrete at early age. This project investigates the use of nanosilica to compensate for such loss of compressive strength. A statistical experimental design involving mixtures of Portland cement, fly ash and nanosilica, in addition to water/binder ratio as an external factor, is proposed to study their combined effect on the compressive strength of concrete. This design allows estimating a cubic regression model that properly accounts for the effects of the mixture components within a constrained experimental region. The range of each factor was selected according to levels normally used in the industry. Finally, an optimisation strategy permits to recommend the use of nanosilica when high percentages of cement replacement by fly ash are present.     

Role of mineral additions in reducing CO2 emission

The influence of the substitution of a part of clinker with the mineral additions, in the process of production of mixed cement, on mechanical characteristics of cement and the reduction of CO₂ emission is researched. Experiments are organized through the production of clinker, which has different phase structures, and cement, using different kinds and amount of mineral additions, with joint grinding and addition to the already ground cement. The most important of the effects analyzed, which include the reduction of thermal and electric energy, is the reduction of CO₂ emission.     

High-strength lightweight concrete made with scoria aggregate containing mineral admixtures

This paper presents a part of the results of an ongoing laboratory work carried out to design a structural lightweight high strength concrete (SLWHSC) made with and without mineral admixtures. In the mixtures, basaltic-pumice (scoria) was used as lightweight aggregate.A control lightweight concrete mixture made with lightweight basaltic-pumice (scoria) containing normal Portland cement as the binder was prepared. The control lightweight concrete mixture was modified by replacing 20% of the cement with fly ash. The control lightweight concrete mixture was also modified by replacing 10% of the cement with silica fume. A ternary lightweight concrete mixture was also prepared modifying the control lightweight concrete by replacing 20% of cement with fly ash and 10% of cement with silica fume. Two normal weight concrete (NWC) were also prepared for comparison purpose.Fly ash and silica fume are used for economical and environmental concerns. Cylinder specimens with 150 mm diameter and 300 mm height and prismatic specimens with dimension 100×100×500 mm were cast from the fresh mixtures to measure compressive and flexural tensile strength. The concrete samples were cured at 65% relative humidity with 20 °C temperature. The density and slump workability of fresh concrete mixtures were also measured.Laboratory test results showed that structural lightweight concrete (SLWC) can be produced by the use of scoria. However, the use of mineral additives seems to be mandatory for production of SLWHSC. The use of ternary mixture was recommended due to its satisfactory strength development and environmental friendliness.     

Rheological properties of grouts with viscosity modifying agents as diutan gum and welan gum incorporating pulverised fly ash

This investigation was undertaken to evaluate the influence of the dosage of the second generation of viscosity modifying agent (diutan gum) on fluidity and rheological parameters of cement-based materials grout compared to welan gum. All grouts were made with 0.40 water-to-binder ratio (W/B). The fresh properties of control grouts made without any viscosity modifying agent (VMA) and with superplasticizer (SP) were compared to those of grouts made with 0.02, 0.04, 0.06 and 0.08% diutan gum by mass of binder. Similar mixes made with welan gum were compared to those containing diutan gums. The effect of admixtures on fluidity and rheological parameters are discussed in this paper. The effect of the replacement of cement by pulverised fly ash (PFA) was also investigated. Grouts with replacements of PFA of 5, 13 and 20% by mass were used with the same W/B. Similar control grouts and mixes incorporated different dosages of PFA made with welan gum were made in order to compare the fluidity and the rheological parameters to the previous grouts made with diutan gum.The results show that the increase of the dosage of diutan gum and welan gum for a given dosage of SP increases significantly the yield value, the apparent and plastic viscosity and reduces the fluidity. With an increase in dosage of SP, the apparent viscosity at low shear rate decreases dramatically than that at high rate of shear rate due to the pseudo-plastic rheology of the grouts containing VMA. Both VMAs exhibited high apparent viscosity values at low shear rates which were attributed to the entanglement and intertwining of VMA polymer chains at low shear rate and association of water between adjacent chains. For a given dosage of VMA, diutan gum showed a high apparent viscosity than welan which could be attributed to the molecular weight and to the long-side chain of diutan gum leading to greater entanglement and intertwining. For any given dosage of SP, the diutan gum exhibited higher yield value and plastic viscosity than welan gum. Diutan gum grouts demonstrate a greater yield value and apparent and plastic viscosity than welan gum for control and PFA grouts. The replacement of cement by PFA resulted in a reduction of yield value and an increase in plastic viscosity.     

基于稳态流变测试的水泥浆体剪切模式研究

采用RHEORIAB QC型旋转黏度计测定不同剪切方式下水泥浆体稳态流变曲线,并用修正宾汉姆流变模型对其进行拟合,研究了剪切方式对水泥浆体稳态流变测试的影响.结果表明:预剪切对水泥浆体动态屈服应力和塑性黏度影响不大.恒定剪切变形速率小于、等于、大于、偏大于水泥浆体结构抗剪切破坏能力时,剪切应力随时间分别先线性增加接着保持同一值、直接保持恒定值、先减小接着保持同一值、轻微增加后达到平衡.随剪切速率增加,水泥浆体在0.1～100 s-1、100～400 s-1、400～600 s-1三个区段依次呈现出剪切变稀、宾汉姆流体、剪切增稠的流变行为.剪切速率变化范围向剪切变稀或剪切增稠段移动,水泥浆体动态屈服应力减小、塑性黏度增大;单个剪切速率的剪切时间越长,水泥浆体动态屈服应力、塑性黏度均越小.     

礁石粉对超高强混凝土工作性能和力学性能的影响研究

采用礁石粉取代部分(0％、10％、20％以及30％)水泥时,对比研究了礁石粉对超高强混凝土(UHSC)流变性能、流动度和强度的影响,利用XRD、DTG方法研究了礁石粉对UHSC水化产物的影响.结果表明,浆体的屈服应力和塑性粘度随礁石粉掺量的增加先减小后增大,礁石粉掺量为10％时的屈服应力和塑性粘度最小分别为2.46 Pa、3.29 Pa·s;掺入适量的(≤20％)礁石粉能提高UHSC的流动度,礁石粉掺量为10％时的UHSC流动度最大为330 mm;30％以内掺入礁石粉能提高UHPC的抗压强度,且对UHSC的3 d抗压强度提高最明显;礁石粉的加入可以显著降低水泥水化放热峰值,礁石粉掺量越大,水化放热峰值降低的越明显,礁石粉的加入能明显推迟水泥水化放热达到峰值的时间;XRD和DTG结果表明礁石粉并不改变水化产物的种类.     

超细粉体对水泥净浆流变行为影响研究

采用截锥圆模法测定不同掺量超细粉体水泥复合浆液的流动度.采用ZNN-D6B型旋转黏度计研究超细玻璃粉和偏高岭土两种超细粉体对水泥净浆流变行为的影响,得到了剪切速率-剪切应力(γ-τ)曲线和剪切速率-表观粘度(γ-μa)曲线,并分别采用宾汉姆模型和赫-巴模型对γ-τ流变曲线进行拟合,得到不同掺量超细玻璃粉-水泥(GP-C)复合浆液和偏高岭土-水泥(MK-C)复合浆液的动切力、塑性粘度、稠度系数和流性指数等流变参数.结果表明:超细粉体的加入降低了复合浆液的流动度.随着掺量的增加,两种复合浆液的宾汉动切力τ0、塑性粘度η、赫-巴动切力τy均逐渐增大,MK-C复合浆液的稠度系数K和流性指数n逐渐减小,GP-C复合浆液的稠度系数K呈现增大-减小-增大的趋势,而流性指数n呈现减小-增大-减小的趋势.所有样本表观粘度μa都随着剪切速率的增大而减小,呈现剪切稀释现象.     

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.