Properties of self-compacting portland pozzolana and limestone blended cement concretes containing different replacement levels of slag

In order to reduce energy consumption and CO₂ emission, and increase production, cement manufacturers are blending or inter-grinding mineral additives such as slag, natural pozzolana, and limestone. This paper reports on the results of an experimental study on the production of self-compacting concrete (SCC) produced with portland cement (PC), portland pozzolana (PPC) and portland limestone (PLC) blended cements. Moreover, the effect of different replacement levels (0–45%) of ground granulated blast furnace slag (GGBFS) with the PPC, PLC, and PC cements on fresh properties (such as slump flow diameter, T ₅₀₀ slump flow time, V-funnel flow time, L-box height ratio, setting time, and viscosity) and hardened properties (such as compressive strength and ultrasonic pulse velocity) of self-compacting concretes are investigated. From the test results, it was found that it was possible to manufacture self-compacting concretes with PPC or PLC cements with comparable or superior performance to that of PC cement. Furthermore, the use of GGBFS in plain and especially blended cement self-compacting concrete production considerably enhanced the fresh characteristics of SCCs.     

Effect of Superfine Slag Powder on HPC Properties

A superfine slag powder (SP) made from granulated blast furnace slab incorporating activators by using sepecial miling technique,was used as supplementary cementitious material in high performance concrete (HPC),replacing part of the mass of normal Portland cement,The effects of the SP on the workability,mechanical and crack self-healing properties of HPC were studied,The hydration process and microstructure characteristics were investigated by X-ray diffraction(XRD) and scanning electron microscopy (SEM) techniques,resectively,The crack self-healing capacity was evaluated by Brazilian test,The test results indicate that the SP has especially supplementary effect on water reducing and excellent property of better control of slump loss ,The concrete flowability increases remarkably with of HPC containing SP are higher than the corresponding strength of the control concrete at all ages,The crack self-healing ability is highly dependent on SP content of HPLC.     

矿物掺合料对聚羧酸减水剂与水泥相容性的影响

高性能减水剂与水泥适应性差会导致混凝土流动性和坍落度损失过快,矿物掺合料将影响高性能减水剂与水泥的相容性。对比研究矿物掺合料种类和掺量对水泥净浆、砂浆和混凝土流动性的影响;采用TOC法测试了矿物掺合料对聚羧酸减水剂吸附量的影响;分析了矿物掺合料影响聚羧酸减水剂与水泥相容性的机理。结果表明,粉煤灰和矿渣对提高水泥净浆流动性具有一定的叠加效应,可用胶砂减水率的加权平均值进行量化;硅灰对水泥浆体流动性的不利影响远大于粉煤灰和矿渣的辅助减水分散作用,不利于改善聚羧酸减水剂与水泥的相容性;粉煤灰和矿渣增加聚羧酸减水剂在水泥体系中的吸附量;粉煤灰和矿渣对聚羧酸减水剂在混凝土中的减水分散效果有改善作用但不显著。     

Influence of superplasticizer type and mix design parameters on the performance of them in concrete mixtures

The use of superplasticizers in concrete manufacture was a milestone in the history of concrete, and this played a central role in the development of high strength and performance concrete. Superplasticizers are admixtures, which are added to concrete mixture in very small dosages. Their addition results in significant increase of the workability of the mixture, in reduction of water/cement ratio or even of cement quantity. Their performance depends on the type of the superplasticizer, the composition of the concrete mixture, the time of addition and the temperature conditions during mixing and concreting.Measurements of workability, slump loss, air content, as well as of strength development have been made to reach a conclusion about superplasticizers performance with the use of two kinds of aggregate: one natural (river) and one crushed limestone. Apart from this, it seems that the quantity of fines in a mixture influences the performance of superplasticizers.     

Effect of repeated dosages of superplasticizers on slump,strength and freeze-thaw resistance of concrete

Superplasticizers, when added to fresh concrete, cause large increases in its slump. However, this increase in slump is not sustained over long periods and within 60 minutes or so the concrete reverts to its original slump. In actual field applications of superplasticizers it may be necessary to add additional dosages to maintain the increased slump. This paper gives results of a laboratory investigation to determine the effect of repeated dosages of superplasticizers on workability, strength and durability of concrete. A series of air-entrained concrete mixes was made at a water/ cement ratio of 0.42 with a slump of 50 mm. Four commonly available superplasticizers were repeatedly added to the concrete, at the manufacture's recommended dosage rates, after completion of initial mixing. This was followed by additional mixing for 2 minutes. The properties of the fresh concrete were determined and test cylinders were cast after the addition of each dosage. Test prisms were also cast for strength and durability studies after the addition of the last dosage. The test results indicate that large increases in slumps of superplasticized concretes can be maintained for several hours by the addition of a second dosage. Apart from one instance, the addition of the third dosage is not considered desirable. The repeated additions of sulphonated melamine- and naphthalene-based superplasticizers caused substantial loss in entrained air content of the concrete; however, for concrete incorporating the lignosulphonate based superplasticizer, the reverse was true. The loss of entrained air adversely affected the performance of the concrete in freeze-thaw tests.     

Effects of mineral admixtures on fresh and hardened properties of self-compacting concretes: binary,ternary and quaternary systems

The paper presented herein investigates the effects of using supplementary cementitious materials in binary, ternary, and quaternary blends on the fresh and hardened properties of self-compacting concretes (SCCs). A total of 22 concrete mixtures were designed having a constant water/binder ratio of 0.32 and total binder content of 550 kg/m³. The control mixture contained only portland cement (PC) as the binder while the remaining mixtures incorporated binary, ternary, and quaternary cementitious blends of PC, fly ash (FA), ground granulated blast furnace slag (GGBFS), and silica fume (SF). After mixing, the fresh properties of the concretes were tested for slump flow time, L-box height ratio, V-funnel flow time, setting time, and viscosity. Moreover, compressive strength, ultrasonic pulse velocity, and electrical resistivity of the hardened concretes were measured. Test results have revealed that incorporating the mineral admixtures improved the fresh properties and rheology of the concrete mixtures. The compressive strength and electrical resistivity of the concretes with SF and GGBFS were much higher than those of the control concrete.     

The effect of chemical admixtures and mineral additives on the properties of self-compacting mortars

Mortar serves as the basis for the workability properties of self-compacting concrete (SCC) and these properties could be assessed by self-compacting mortars (SCM). In fact, assessing the properties of SCM is an integral part of SCC design. The objective of this study was to evaluate the effectiveness of various mineral additives and chemical admixtures in producing SCMs. For this purpose, four mineral additives (fly ash, brick powder, limestone powder, and kaolinite), three superplasticizers (SP), and two viscosity modifying admixtures (VMA) were used. Within the scope of the experimental program, 43 mixtures of SCM were prepared keeping the amount of mixing water and total powder content (portland cement and mineral additives) constant. Workability of the fresh mortar was determined using mini V-funnel and mini slump flow tests. The setting time of the mortars, were also determined. The hardened properties that were determined included ultrasonic pulse velocity and strength determined at 28 and 56 days. It was concluded that among the mineral additives used, fly ash and limestone powder significantly increased the workability of SCMs. On the other hand, especially fly ash significantly increased the setting time of the mortars, which can, however, be eliminated through the use of ternary mixtures, such as mixing fly ash with limestone powder. The two polycarboxyl based SPs yield approximately the same workability and the melamine formaldehyde based SP was not as effective as the other two.     

Effects of CuO nanoparticles on compressive strength of self-compacting concrete

In the present study, the compressive strength, thermal properties and microstructure of self-compacting concrete with different amounts of CuO nanoparticles have been investigated. CuO nanoparticles with an average particle size of 15 nm were added to self-compacting concrete and various properties of the specimens were measured. The results indicate that CuO nanoparticles are able to improve the compressive strength of self-compacting concrete and reverse the negative effects of superplasticizer on compressive strength of the specimens. CuO nanoparticles as a partial replacement of cement up to 4 wt.% could accelerate C–S–H gel formation as a result of the increased crystalline Ca(OH)₂ amount at the early ages of hydration. Increasing CuO nanoparticle content to more than 4 wt.%, causes reduced compressive strength because of unsuitable dispersion of nanoparticles in the concrete matrix. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that CuO nanoparticles up to 4 wt.% could improve the mechanical and physical properties of the specimens. Finally, CuO nanoparticles improved the pore structure of concrete and caused shifting of the distributed pores from harmless to low harm.     

Properties of self-compacting concrete prepared with recycled glass aggregate

The effects of recycled glass (RG) cullet on fresh and hardened properties of self-compacting concrete (SCC) were investigated. RG was used to replace river sand (in proportions of 10%, 20% and 30%), and 10 mm granite (5%, 10% and 15%) in making the SCC concrete mixes. Fly ash was used in the concrete mixes to suppress the potential alkali-silica reaction. The experimental results showed that the slump flow, blocking ratio, air content of the RG–SCC mixes increased with increasing recycled glass content. The compressive strength, tensile splitting strength and static modulus of elasticity of the RG–SCC mixes were decreased with an increase in recycled glass aggregate content. Moreover, the resistance to chloride ion penetration increased and the drying shrinkage of the RG–SCC mixes decreased when the recycled glass content increased. The results showed that it is feasible to produce SCC with recycled glass cullet.     

Filling ability and plastic settlement of self-compacting concrete

The use of self-compacting concrete (SCC) facilitates the placing of concrete by eliminating the need for compaction by vibration. Given the highly flowable nature of such concrete, care is required to ensure excellent filling ability and adequate stability. This is especially important in deep structural members and wall clements where concrete can block the flow, segregate and exhibit bleeding and settlement which can result in local defects that can reduce mechanical properties, durability and quality of surface finish.This paper shows results of an investigation of fresh properties of self-compacting concrete, such as filling ability measured by slump flow and flow time (measured by Orimet) and plastic fresh settlement measured in a columin. The SCC mixes incorporated various combinations of fine inorganic powders and admixtures. The slump flow of all SCCs was greater than 580 mm and the time in which the slumping concrete reached 500 mm was less than 3 s. The flow time was less than 5 s. The results on SCCs were compared to a control mix. The compressive strength and splitting tensile strength of SCCs were also measured.The effects of water/powder ratio, slump and nature of the sand on the fresh settlement were also evaluated. The volume of coarse aggregate and the dosage of superplasticizer were kept constant. It can be concluded that the settlement of fresh self-compacting concrete increased with the increase in water/powder ratio and slump. The nature of sand influenced the maximum settlement.     

Influences of superplasticizer modification and mixture composition on the performance of self-compacting concrete at varied ambient temperatures

The fresh behaviour of self-compacting concrete (SCC) at varying temperatures differs from that of normal vibrated concrete. This is because the rheology of SCC depends not only on degree of cement hydration, but also on the adsorption of superplasticizers – mostly polycarboxylate based polymers (PCE) -, which is affected by the time and hydration progress. Due to the variety of PCEs and mixture compositions for SCC a prediction of the rheology at varying temperatures is complicated. The charge densities of PCEs as well as the water to solid ratio in the paste are identified to be the main decisive parameters for robust fresh concrete properties.Rheometric concrete investigations with different SCC mixture compositions and varied anionic charge densities of the PCE were conducted. SCC which is rich in powder components showed robust performance at low temperatures while SCC with low powder content was favourable at high temperatures. High charge density PCE pointed out to be very robust at low temperatures but at high temperatures it significantly reduced the flow retention. Low charge density PCE could not generate self-compacting properties at low temperatures but retained the flow performance over sufficiently long time. Based on considerations about particle interactions and adsorption mechanisms of PCEs, the relevant processes are explained and options for the development of robust mixture compositions for individual temperature ranges are itemised.     

掺加改性淀粉制备聚羧酸减水剂及其应用

选取经过降解处理的羧甲基淀粉醚(CMS-Na)代替部分异戊烯基聚氧乙烯醚(TPEG)制备一种新型聚羧酸系减水剂(PC2),利用水泥净浆单组分试验得出CMS-Na对TPEG的最佳替代量为15%。另外,用红外光谱(FTIR)对CMS-Na及聚羧酸减水剂的分子结构进行了表征。结果表明,掺加CMS-Na合成的PC2不仅降低了原材料的成本,而且具有良好的分散性和保塑性,同时不影响混凝土强度。     

Mix design method for self compacting metakaolin concrete with different properties of coarse aggregate

This study deals with a proposed mix design method for SCC utilizing different properties of coarse aggregate. The work was conducted in three phases, i.e. paste, mortar and concrete to facilitate the mix design process. Initial investigation on cement paste determined the basis for water cement ratio and superplasticizer dosage for the concrete. For the study on mortar, metakaolin (MK) as pozzolan was used at replacement levels of 5%, 10%, 15%, and 20% by weight of cement. Self compactability of mortars was obtained by adding suitable materials such as mineral admixtures and superplasticizer which provided a sufficient balance between flowability and viscosity of the mix. The optimum MK replacement level for cement was 10% from the viewpoint of workability and strength. Flowability of mortar decreased with the use of metakaolin. Moreover, strength of mortar increased when the optimum replacement level of pozzolan was used. Different fresh concrete tests were adopted. The results obtained for fresh concrete properties showed that flowability of concrete increased with increase flowability of mortar. The mixes which contained coarse aggregate with lower volume, small size, and continuous grading affected positively the fresh properties of SCC. Finally, the mix design method used was successful in producing SCC with different coarse aggregate properties.     

Preparation of Ultra-High Performance Concrete with common technology and materials

The technology development of concrete and demand for high strength construction materials give momentum to the development of Ultra-High Performance Concrete (UHPC). Current UHPC preparation methods require costly materials and relatively sophisticated technology. To overcome these weaknesses, this paper focused on the preparation of UHPC with common technology and ordinary raw materials. Influence of binder content, water/binder ratio, ground granulated blastfurnace slag (GGBS) content, and limestone powder (LP) replacement on fluidity and compressive strength of concrete were researched, respectively. The test results show that the addition of superplasticizer and fine mineral additives enabled the UHPC to be produced at an extremely low water/binder ratio of 0.14-0.18, achieving excellent workability with a maximum slump of 268 mm and compressive strengths of 175.8 MPa at 90 d and 182.9 MPa at 365 d.     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

Evaluating and forecasting the initial and final setting times of self-compacting concretes containing mineral admixtures by neural network

An experimental study was conducted to investigate the effects of using binary, ternary, and quaternary cementitious blends of portland cement (PC), fly ash (FA), ground granulated blast furnace slag (GBS), silica fume (SF), and metakaolin (MK) on initial and final setting times of self-compacting concretes (SCCs). For this purpose, a total of 65 SCC mixtures were prepared at two different water binder ratios. Furthermore, based on the experimental results, neural network (NN) model-based explicit formulations were developed to predict the initial and final setting times of SCCs in terms of the amount of concrete constituents, namely mixing water, PC, FA, GBS, SF, MK, fine (fa) and coarse (ca) aggregates, and superplasticizer (SP). The test results have revealed that the mineral admixtures were very effective on the initial and final setting times of SCCs. Besides, it was found that the model developed by using NN seemed to have a high prediction capability of initial and final setting times of SCCs.     

The effect of blast furnace slag on the self-compactability of pumice aggregate lightweight concrete

This paper presents the results of an experimental study of the effects of blast furnace slag, different water/(cement + mineral additive) ratios and pumice aggregates on some physical and mechanical properties of self-compacting lightweight aggregate concrete. In this study, pumice was used as lightweight aggregate. Several properties of self-compacting pumice aggregate lightweight concretes, such as unit weight, flow diameter, T50 time, flow diameter after an hour, V-funnel time, and L-box tests, 7, 28, 90 and 180-day compressive strength, 28-day splitting tensile strength, dry unit weight, water absorption, thermal conductivity and ultrasonic pulse velocity tests, were conducted. For this purpose, 18 series of concrete samples were prepared in two groups. In the first group, pumice aggregate at 100% replacement of natural aggregate was used in the production of self-compacting lightweight aggregate concrete with constant w/(c + m) ratios as 0.35, 0.40, and 0.45 by weight. Furthermore, as a second group, pumice aggregate was used as a replacement of natural aggregate, at the levels of 0, 20, 40, 60, 80, and 100% by volume. Flow diameters, T50 times, paste volumes, 28-day compressive strengths, dry unit weights, thermal conductivities and ultrasonic pulse velocity of self-compacting lightweight aggregate concrete were obtained over the range of 600–770 mm, 3–9 s, 435–540 l/m ³, 10.6–65.0 MPa, 845–2278 kg/m ³, 0.363–1.694 W/mK and 2617–4770 m/s respectively, which satisfies not only the strength requirement of semi-structural lightweight concrete but also the flowing ability requirements and thermal conductivity requirements of self-compacting lightweight aggregate concrete.     

Utilization of ceramic waste as fine aggregate within Portland cement and fly ash concretes

The aim of this research work was to investigate the feasibility of using ceramic waste and fly ash to produce mortar and concrete. Ceramic waste fragments obtained from local industry were crushed and sieved to produce fine aggregates. The measured concrete properties demonstrate that while workability was reduced with increasing ceramic waste content for Portland cement concrete and fly ash concrete, the workability of the fly ash concrete with 100% ceramic waste as fine aggregate remained sufficient, in contrast to the Portland cement control concrete with 100% ceramic waste where close to zero slump was measured. The compressive strength of ceramic waste concrete was found to increase with ceramic waste content and was optimum at 50% for the control concrete, dropping when the ceramic waste content was increased beyond 50%. This was a direct consequence of having a less workable concrete. However, the compressive strength in the fly ash concrete increased with increasing ceramic waste content up to 100%. The benefits of using ceramic waste as fine aggregate in concrete containing fly ash were therefore verified.     

保水降温功能水泥混凝土铺面材料组成设计与性能研究

将水泥、粉煤灰和磨细高炉矿渣作为保水材料灌注于多孔水泥混凝土母体中,形成具有保水降温功能的铺面材料。分别提供了多孔水泥混凝土母体和保水材料的设计方法,并成型试件对保水铺面水泥混凝土材料的强度、降温效果和抗冻性进行了测试。实验结果表明设计的多孔水泥混凝土母体和保水材料均满足施工和功能要求,成型的保水降温功能水泥混凝土试件28d抗压强度和抗折强度分别能够达到27.7和38.2MPa;在最高气温为33℃的测试条件下,其表面最高温度比普通水泥混凝土降温7℃左右,但随着水分的减少降温效果变差;此外,冻融后保水降温水泥混凝土抗压强度会下降,但不明显。     

Properties of self-compacting concrete containing class F fly ash

An experimental program was carried out to study the properties of self-compacting concrete (SCC) made with Class F fly ash. The mixes were prepared with five percentages of class F fly ash ranging from 15% to 35%. Properties investigated were self-compactability parameters (slump flow, J-ring, V-funnel, L-box and U-box), strength properties (compressive and splitting tensile strength), and durability properties (deicing salt surface scaling, carbonation and rapid chloride penetration resistance).