Rheological properties of cement mixes: V. The effects of time on viscometric properties of mixes containing superplasticizers; Conclusions

The effects of sulfonated naphthalene- and melamine-formaline condensates upon the rheologic properties of cement pastes and slurries have been investigated. Coaxial cylindrical viscometer measurements were made, recording shear stress-shear rate relationships and defining yield stress and plastic viscosity. The changes of these functions with time were investigated, and were related to admixture type and concentration, cement type, and volume concentration of cement. The mechanisms of action of the superplasticizers are discussed.     

Rheological properties of carbon mixes at low shear rates using a capillary rheometer

A capillary rheometer is used to measure the rheological properties of green carbon mixes consisting of petroleum coke and carbon black as filler and pitch tar as binder. It has been shown that in the low shear rate range (0·3 to 2·0 sec^?1), the carbon mixes behave as Bingham body with yield stress of 6 × 10⁵ dyn/cm² and plastic viscosity of 2 × 10⁶ poise.     

Rheological properties of cement mixes: II. Zeta potential and preliminary viscosity studies

The effects of superplasticizing admixtures upon rheological properties of cement mixes have been investigated. Their effects upon the zeta potential generated at the interface between cement particle surfaces and the admixture-containing liquid were studied by electrophoretic and streaming potential techniques. Comparisons were made between the above results and the results of mortar flow measurements; the results of rotational viscometric measurements on slurries also revealed a strong influence of the admixtures upon the apparent viscosity. Significant correlations are made among the results of zeta potential, flow properties and adsorption isotherm measurements.     

Rheological properties of carbon mixes at very low shear rates using a capillary rheometer—III

A capillary rheometer has been used to determine the rheological properties of carbon mixes consisting of petroleum coke as filler and coal tar pitch as binder. It is shown that carbon mixes behave as Bingham materials with definite yield stresses. The yield stress was found to be a general property of all carbon mixes and its value is independent of the size of the capillary die. It was also seen that extrusion at low shear rates through big diameter capillaries results in slipflow. The slipflow occurs when the applied stress is somewhat below the yield stress, the material then extrudes without the formation of a core which otherwise would cause cracks in the product after baking. This explains why big diameter rods are generally extruded at very low speeds in usual manufacturing process. The modified Buckingham-Reiner equation has been applied to the case of slipflow and the values of yield stress and plastic viscosity calculated. These values agree well with those obtained from the consistency curve.     

Evaluation of natural zeolite as a viscosity-modifying agent for cement-based grouts

The effects of natural zeolite on the rheological and workability properties of the grout mixtures were studied. Setting times of grouts were also determined as part of the experimental study. For comparison, grout mixtures were also prepared with a commercially available viscosity modifying admixture (VMA). The experimental results show that addition of natural zeolite modifies both the rheological and workability properties of grouts. For a constant superplasticizer (SP) content, an increase in the zeolite amount significantly increases the yield stress, the apparent and plastic viscosity, and reduces the fluidity and deformability. Moreover, an increase in the amount of SP causes a significant reduction in both the yield stress and plastic viscosity of the grouts. It was also observed that, grouts prepared with natural zeolite addition have a pseudo-plastic behavior, and shear-thinning behavior increases with an increase in the zeolite amount. Therefore, it has been shown that using natural zeolite as a VMA it is possible to obtain grouts that have satisfactory rheological properties, especially if natural zeolite is used in combination with a superplasticizer.     

Rheological properties of cement mixes: IV. Effects of superplasticizers on viscosity and yield stress

The effect of sulfonated naphthalene- and melamine-formaline condensates upon the viscometric properties of cement pastes and slurries has been investigated. Plastic viscosity and yield stress were determined from coaxial cylinder viscometer measurements. These were related to admixture type and concentration, cement type, and to the volume concentration of cement in the mix.     

Cement-based mixes: Shearing properties and pore pressure

This study presents original results on the rheological measurement of concrete mixes. It focuses on how to determine their mechanical and physical behavior under shearing stress. More specifically, the influence of aggregate content on shearing properties is studied. A vane rheometer was developed to characterize fresh cement-based materials. In addition to the conventional concrete rheometer, a special hydraulic pressure transducer was fitted to the container to monitor the pore water pressure variation while shearing the material. Experiments on cement paste, mortar, and concrete bring a new approach to help us understand the behavior of fresh-state mixes. The results show 1) a correlation between water pore pressure and torque applied on the vane; 2) a critical sand volume fraction, ?_c, as a limit between colloidal interaction behavior and frictional behavior in mortars; beyond this critical fraction, a leap in yield stress and a drop in pore pressure due to granular dilatancy are noticed; 3) the granular content clearly influences the increase in yield stress of the cement mixes: above ?_c, this increase becomes negligible.     

Influence of time addition of superplasticizers on the rheological properties of fresh cement pastes

It is well known that the fluidity and the fluidity loss of fresh cement pastes are affected by the kind and the time of addition of organic admixtures. The influence of the time addition of two chemical admixtures, namely, melamine formaldehyde sulfonate (MFS) and naphthalene formaldehyde sulfonate (NFS), on the rheological properties of ordinary Portland and sulfate-resisting cement pastes through the first 120 min of hydration was investigated. The admixture addition was delayed by 0, 5, 10, 15, 20, and 25 min. Shear stress and apparent viscosity of the cement pastes were determined at different shear rates (3-146 s⁻¹) and hydration times of 30, 60, 90, and 120 min. The concentration of Ca²⁺ and the combined water content of the cement pastes were determined after 120 min. Yield stress and plastic viscosity values were also determined by using the Bingham model. The results show that an increase in the addition time of the admixture reduces the shear stress, the yield stress, and the plastic viscosity of the cement pastes at the early ages (15 min) as well as at later early ages (120 min). The optimum delaying time of admixture addition is found to be 10-15 min. This time does not depend on the cement and superplasticizer type.     

搅拌过程和流变性对水泥基材料中纤维分布及力学性能影响

纤维增强水泥基设计复合材料( ECC)具有高延性特征,而成型过程影响纤维在水泥基体内分布状态,进而影响ECC获得高延性性能的稳定性。本文综述了ECC搅拌过程和拌合状态下的流变性能对纤维分布的影响,重点分析了塑性黏度和屈服应力对纤维分布及力学性能的影响。结果表明：后加纤维的搅拌过程是ECC成型过程中纤维分布的最优方式;良好的塑性黏度是保证纤维均匀分布的关键,屈服应力影响纤维分布及取向分布;综合调整ECC的流变性可以保证纤维均匀分布,使硬化后ECC获得稳定的高延性。     

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.     

锂渣掺量对水泥-减水剂浆体流变特性和混凝土性能的影响

本文研究了锂渣掺量对水泥-减水剂浆体流变特性、新拌混凝土工作性及硬化混凝土强度的影响。从紧密堆积理论和固体颗粒体积分数角度解释了锂渣掺量对水泥-减水剂浆体流变性能的影响。结果表明：锂渣水化初始的屈服应力和塑性黏度均随锂渣掺量的增加而增大，流变性能劣化。新拌混凝土的工作性与锂渣掺量呈负相关；随锂渣掺量的增加，7 d抗压强度不断降低，28 d抗压强度呈现出先增后降的趋势。     

锭模用耐火涂料的流变性质与其工艺性能的关系

研究了水基锭模耐火涂料的流变学性质与其工艺性能之间的关系。实验结果表明，使用性能良好的钨模耐火涂料在低剪切条件下，应具有较大的表现粘度与屈服应力，以及较小的塑性粘度和适当的触变性。     

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.     

Rheological and mechanical properties of composites made from wood flour and recycled LDPE/HDPE blend

The effect of compounding method is studied with respect to the rheological behavior and mechanical properties of composites made of wood flour and a blend of two main components of plastics waste in municipal solid waste, low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The effects of recycling process on the rheological behavior of LDPE and HDPE blends were investigated. Initially, samples of virgin LDPE and HDPE were thermo-mechanically degraded twice under controlled conditions in an extruder. The recycled materials and wood flour were then compounded by two different mixing methods: simultaneous mixing of all components and pre-mixing, including the blending of polymers in molten state, grinding and subsequent compounding with wood flour. The rheological and mechanical properties of the LDPE/HDPE blend and resultant composites were determined. The results showed that recycling increased the complex viscosity of the LDPE/HDPE blend and it exhibited miscible behavior in a molten state. Rheological testing indicated that the complex viscosity and storage modulus of the composites made by pre-mixing method were higher than that made by the simultaneous method. The results also showed that melt pre-mixing of the polymeric matrix (recycled LDPE and HDPE) improved the mechanical properties of the wood–plastic composites.     

减水剂的加入时间对新拌水泥浆体流变性能的影响

研究了三聚氰胺甲醛磺酸盐(MFS)减水剂的掺加时间对普通硅酸盐水泥浆体在初始120 min的水化时间内流变性能的影响,研究中MFS的后掺时间为0 min、5 min、10 min、15 min、20 min和25 min。检测了在不同减切速率(3～147 s-1)下水泥浆体水化30 min和120 min时的剪切应力和表观粘度。测定了水化120 min后的水泥浆体的Ca2+浓度和化学结合水。结果表明:推迟减水剂的后掺时间降低了水泥浆体在120 min内的屈服应力和表观粘度,减水剂MFS的最佳后掺时间为10～15 min。     

Shear flow rheological properties,fiber damage,and mastication characteristics of aramid-, glass-, and cellulose-fiber-reinforced polystyrene melts

An experimental study of the viscosity and principal normal stress difference of a polystyrene melt filled with aramid (Kevlar), glass, and cellulose fibers is reported. The influence of loading level and mastication on the rheological properties is discussed. The effects of mixing and mastication on fiber damage are considered. Glass fibers break down rapidly to very small aspect ratios, while aramid shows a “kinked” structure, with kinks occurring every 100 μm. A mechanism is proposed for fiber breakage based on buckling during rotation in shear flow. It is found that addition of fibers increases the viscosity in the same manner as a reduction in temperature, and data may be superposed by reduced plotting. This indicates that the viscosity increase is due solely to enhanced viscous dissipation in the matrix and not to interparticle forces as is the case with smaller particles. The principal normal stress difference increases at fixed shear stress with fiber loading. The extent of increase depends upon fiber loading, aspect ratio, and modulus.     

Rheology of ordinary and low-impact environmental concretes

This study deals with the rheological properties of concrete mixtures incorporating various types of mineral additions as a partial replacement of cement in order to produce a low-impact environmental concrete. The control mixture contained only Portland cement as the binder, while the remaining mixtures incorporated binary cementitious blends of slag, limestone filler, and fly ash with different rates of replacement. After mixing, the plastic viscosity and yield stress of the concretes were evaluated at different slump values using a rheometer apparatus. The results showed that the type of mineral additions and the rate of substitution affect the rheological parameters of low-impact environmental concrete. Indeed, increasing the degree of substitution leads to an increase in the plastic viscosity of the concrete made with different types of additions used in this study.     

粒度分布对超低水泥刚玉质浇注料流变性的影响

用浇注料流变仪研究了粒度分布对超低水泥刚玉质浇注料流变性的影响。结果表明 :粒度分布对超低水泥浇注料的流变性影响较大。随着粒度分布系数 (q)的减小 (从 0 .2 9、0 .2 6到 0 .2 3) ,浇注料的剪切应力、粘度和屈服应力增加 ,需水量上升 ,说明流变性变差。以 2 %的SiO2 微粉等量替代q =0 .2 3的浇注料中的Al2 O3微粉后 ,试样的流变性得到明显改善 ,更适合用于泵送施工 :浇注料的需水量减少 ,自流值提高。     

Effects of a water-retaining agent on the rheological behaviour of a single-coat render mortar

The effects of a water-retaining admixture on the rheological properties of a cement-based render mortar were studied. This agent, based on a cellulose ether compound, was introduced in contents up to 0.2 wt.%.Rheological behaviour was studied with a rheometer for mortars using two different speed profiles. First, the step profile allowed observing the variation of g and h parameters with the water-retaining agent content, g and h being directly related to yield stress and plastic viscosity. Second, the dwell profile allowed the study of the rheological behaviour variation with time, particularly the study of structural breakdown and reconstruction phenomena. These phenomena could be followed through the evolution of the hysteresis area in the flow curves. It was also possible to conclude that this admixture has a thickening effect except for low amounts (≤ 0.08%) and that it promotes structural breakdown together with a secondary effect of retarding the setting time.     

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.