Effect of cement type on the resistance of concrete against chloride penetration

In chloride containing environment, chloride permeability of concrete is an important parameter affecting the service life of concrete structures. The primary objective of this experimental study was to study the effect of cement types on the resistance of concrete against chloride penetration for given compressive strength classes. These cements included two different types of granulated blast-furnace slag cement (CEM III/A 32.5N and CEM III/A 42.5N), a sulfate resisting cement (SRC 32.5), and a Portland cement blended with fly ash; all of which compared to an ordinary Portland cement (CEM I 42.5R). For each binder type, four concretes at different strength classes were produced and as a result 20 mixtures were obtained. Rapid chloride ion penetration tests according to ASTM C 1202 were conducted. In addition, electrical resistivity and capillary water absorption tests were carried out. In order to characterize the concrete quality, compressive strength of the specimens were also obtained. The test results clearly demonstrated that the blast-furnace slag cements have the highest resistance against chloride penetration, while the pure Portland cement and sulfate resisting cement have the lowest resistance. Concretes produced with the sulfate resisting cement had substantially higher capillary sorption compared to other mixtures. Test results confirmed the strong relationship between the chloride permeability and electrical resistivity.     

水泥土无侧限抗压强度和电阻率的试验研究

以两种类型的水泥（普通硅酸盐水泥和矿渣硅酸盐水泥）搅拌形成的水泥土试块为研究对象,通过室内试验定量分析了其无侧限抗压强度、电阻率、龄期之间的相互关系,试验结果表明：这两种水泥土试块的无侧限抗压强度和电阻率均随着龄期对数的增加成线性函数增大,无侧限抗压强度与其电阻率成线性增长关系。     

Effects of fineness of cement on polynaphthalene sulfonate based superplasticizer–cement interaction

The effects of fineness of portland cement procured from six different Turkish cement plants, on superplasticizer/cement interaction were investigated. CEM I 42.5 type portland cements (PC) were ground into different finenesses ranging from 280 to 550 m²/kg Blaine values. The effects of PC fineness on initial fluidity and fluidity loss of superplasticized cement paste were evaluated. It was found that increasing the Blaine fineness of incompatible cement up to a certain level reduced the viscosity of cement pastes but had no marked effect on the yield stress of the paste mixtures. Nevertheless, flow loss and also saturation point at 60 min increased with increasing the cement fineness. In other words, pastes with lower viscosity can be produced by using finer cement and more superplasticizer.     

Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures

Drying shrinkage can be a major reason for the deterioration of concrete structures. The contraction of the material is normally hindered by either internal or external restraints so that tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The present study investigated compressive strength and particularly drying shrinkage properties of self-compacting concretes containing binary, ternary, and quaternary blends of Portland cement, fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), and metakaolin (MK). For this purpose, a total of 65 self-compacting concrete (SCC) mixtures were prepared at two different water to binder ratios. It was observed that drying shrinkage lessened with the use of FA, GGBFS, and MK while incorporation of SF increased the drying shrinkage.     

Effect of electric arc furnace dust on the properties of OPC and blended cement concretes

This paper presents results of a study conducted to evaluate the mechanical properties and durability characteristics of ordinary Portland cement (OPC) and blended cement (silica fume and fly ash) concrete specimens prepared with electric arc furnace dust (EAFD). Concrete specimens were prepared with and without EAFD. In the silica fume cement concrete, silica fume constituted 8% of the total cementitious material while fly ash cement concrete contained 30% fly ash. EAFD was added as 2% replacement of cement in the OPC concrete and 2% replacement of the total cementitious content in the blended cement concretes. Mechanical properties, such as compressive strength, drying shrinkage, initial and final setting time, and slump retention were determined. The durability characteristics were evaluated by measuring water absorption, chloride permeability, and reinforcement corrosion. The initial and final setting time and slump retention increased due to the incorporation of EAFD in both OPC and blended cement concretes. The drying shrinkage of EAFD cement concrete specimens was more than that of concrete specimens without EAFD. The incorporation of EAFD was beneficial to OPC concrete in terms of strength gain while such a gain was not noted in the blended cement concretes. However, the strength differential between the blended cement concretes with EAFD and the corresponding concretes without EAFD was not that significant. The water absorption and chloride permeability, however, decreased due to the incorporation of EAFD in both the OPC and blended cement concretes. The corrosion resistance of OPC and blended cement concrete specimens increased due to the addition of EAFD.     

Properties of self-compacting concretes made with binary,ternary, and quaternary cementitious blends of fly ash,blast furnace slag,and silica fume

Self-compacting concretes (SCCs) have brought a promising insight into the concrete industry to provide environmental impact and cost reduction. However, the use of ternary and especially quaternary cementitious blends of mineral admixtures have not found sufficient applications in the production of SCCs. For this purpose, an experimental study was conducted to investigate properties of SCCs with mineral admixtures. Moreover, durability based multi-objective optimization of the mixtures were performed to achieve an optimal concrete mixture proportioning. A total of 22 concrete mixtures were designed having a constant water/binder ratio of 0.44 and a total binder content of 450 kg/m³. The control mixture included only a 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 (S), and silica fume (SF). Fresh properties of the SCCs were tested for slump flow diameter, slump flow time, L-box height ratio, and V-funnel flow time. Furthermore, the hardened properties of the concretes were tested for sorptivity, water permeability, chloride permeability, electrical resistivity, drying shrinkage, compressive strength, and ultrasonic pulse velocity. The results indicated that when the durability properties of the concretes were taken into account, the ternary use of S and SF provided the best performance.     

The effect of Persian Gulf tidal zone exposure on durability of mixes containing silica fume and blast furnace slag

In this research the performance of cement paste and concrete mixes incorporating 7% and 10% of silica fume (SF) as a cement replacement was investigated in three exposure conditions. The results showed that plain type II portland cement performed better than blended SF cement under cyclic wetting and drying conditions. Silica fume specimens under cyclic wetting and drying conditions in simulated seawater exhibited higher strength loss compared to plain type II portland cement where cured under potable water. In addition, the greater the silica fume amount used in the mixes, the more the capillary water absorption under tidal zone exposure or/and under wetting and drying simulation. Further, the ternary blended ground granulated blast furnace slag (GGBS) mix was the worst performing mix in all exposure conditions.     

碱激发矿渣混凝土干缩特性研究

该文研究了水胶比、激发剂种类、碱当量不同情况下的碱激发矿渣混凝土的干缩性能,并与普通硅酸盐水泥混凝土的干缩性能进行对比。结果表明:碱激发矿渣混凝土比普通硅酸盐水泥混凝土干缩大,其干缩率随水灰比的增大而减小;水玻璃激发的碱激发矿渣混凝土干缩率最大;随碱当量增大,碱激发矿渣混凝土的干缩逐渐增大;采用水玻璃作为激发剂,碱激发矿渣混凝土的干缩率随水玻璃模数的增大而增大。     

Optimizing the compressive strength of concrete containing micro-silica,nano-silica,and polypropylene fibers using extreme vertices mixture design

Many studies have evaluated the effects of additives such as nano-silica (NS), micro-silica (MS) and polymer fibers on optimizing the mechanical properties of concrete, such as compressive strength. Nowadays, with progress in cement industry provides, it has become possible to produce cement type I with strength classes of 32.5, 42.5, and 52.5 MPa. On the one hand, the microstructure of cement has changed, and modified by NS, MS, and polymers; therefore it is very important to determine the optimal percentage of each additives for those CSCs. In this study, 12 mix designs containing different percentages of MS, NS, and polymer fibers in three cement strength classes(CSCs) (32.5, 42.5, and 52.5 MPa) were designed and constructed based on the mixture method. Results indicated the sensitivity of each CSCs can be different on the NS or MS in compressive strength of concrete. Consequently, strength classes have a significant effect on the amount of MS and NS in mix design of concrete. While, polymer fibers don’t have significant effect in compressive strength considering CSCs.     

Air void system and frost-salt scaling of concrete containing slag-blended cement

The experimental investigation on the frost-salt scaling resistance of air-entrained concrete containing CEM II/B-S 42.5N and CEM III/A 42.5N-HSR/NA slag-blended cements was performed. The air void system in concrete was evaluated in fresh concrete using AVA and in hardened concrete using an automated image analysis procedure. The mass of scaled material was increased for an increased slag content, in spite of increased compressive strength and flexural strength, decreased water absorption and decreased depth of water penetration of concrete. Increasing slag content resulted in a decrease of the total volume of air in hardened concrete and in a corruption of the air void system exhibited by a decrease of micropores content. The increase of mass of scaled material was proportional to the increase of the spacing factor of air voids, except for CEM III/A cement concrete exhibiting accelerated scaling.     

Prüfkörperabdichtung und der Wasserabsorptionskoeffizient von mit Polypropylenfasern modifizierten Zementmörteln

Insulation of samples and water sorption coefficient of cement mortars modified with polypropylene fibres. In the following paper are shown results of water capillary suction in cement mortars prepared in accordance with 18 different recipes. All the mortars were prepared using natural quartz sand 0 to 2 mm. The mortars were varied with the use of two different cements and two different water‐cement ratios w/c, namely clean cement CEM I 42.5 R at w/c = 0.55 and ash cement CEM II/B‐V 32.5 R at w/c = 0.55 and w/c = 0.45. These mortars were modified by adding three types of polypropylene fibres with five lengths ranging from 3 to 38 mm. All samples were insulated against humidity on the side surfaces to ensure the one‐way water flow during the execution of this experiment. In relation to each type of mortar two different types of insulation were used: a silicone coat and polyethylene foil. The comparative analysis received served to evaluate the scale of reaction to the sorption coefficient A of such factors as: the type of cement, the w/c ratio, the type and length of fibres and the type of humidity insulation. It appeared that this last factor exerted a major effect on the course of the process, and equally on the A parameter when described in terms of quantity.     

Early age deformations of concrete with high content of mineral additions

Under the project “EcoBéton” (Green concrete) funded by the French National Agency (ANR), concrete mixtures with a high quantity of mineral additions, such as blast-furnace slag and fly ash were studied. A first approach to quantify their cracking risk was to measure their plastic shrinkage evolution. In parallel, the evolution of other parameters such as setting, capillary depression and porosity were also monitored to relate this deformation to the evolution of the microstructure of the studied mixtures. Setting monitoring by means of ultrasonic measurements allows obtaining significant macroscopic information such as hardening process and rigidity evolution. The correlation between these different parameters shows that the plastic shrinkage evolution can be divided into three phases driven by different mechanisms. Moreover, it appears that the use of mineral additions has an effect on the plastic shrinkage behaviour, but this impact is not proportional to the percentage of additions. It depends on the hydration process and the microstructure of the cementitious materials. So, it seems that an optimum content of cement replacement by mineral additions must be sought to limit the development of plastic shrinkage of concretes with mineral additions at early age. However, a high rate of substitution of cement may affect the early age compressive strength of the concrete. So these mixtures were also optimised to obtain a significant compressive strength at an early age, but this optimisation leads to a higher risk of cracking for some of them.     

Effect of curing methods on the properties of plain and blended cement concretes

This paper reports result of a study conducted to investigate the effect of curing methods on the properties of plain and blended cement concretes. The concrete specimens were prepared with Type I, silica fume, and fly ash cement concretes. They were cured either by covering with wet burlap or by applying two types of curing compounds, namely water-based and acrylic-based. The effect of curing methods on the properties of plain and blended cement concretes was assessed by measuring plastic and drying shrinkage, compressive strength, and pulse velocity. Results indicated that the strength development in the concrete specimens cured by covering with wet burlap was more than that in the specimens cured by applying water – and acrylic-based curing compounds. Concrete specimens cured by applying curing compounds exhibited higher efficiency in decreasing plastic and drying shrinkage strain than specimens cured by covering with wet burlap. The performance of acrylic-based curing compound was better than that of water-based curing compound. The data developed in this study indicate that curing compounds could be utilized in situations where curing with water is difficult. Among the two curing compounds investigated, acrylic-based curing compound performed better than the water-based curing compound.     

水灰比、胶集比及水泥浆量对混凝土塑性收缩裂缝的影响

新拌混凝土浇注成形后在模拟环境条件下进行试验。固定单方混凝土用水量的试验结果表明:较低和较高水灰比混凝土拌合物在塑性阶段不易开裂,而中间某一水灰比时对应的裂缝面积最大;这一最大裂缝面积对应的中间水灰比为0.4或0.45左右。胶集比或水泥浆量对混凝土塑性收缩裂缝的影响与水灰比的情况相似。水分蒸发速率随水灰比的增大而增大。     

Effect of superplasticizer on plastic shrinkage of plain and silica fume cement concretes

Four types of superplasticizers were used in conjunction with three types of silica fume to prepare cement concrete slab specimens that were utilized to measure plastic shrinkage strain and time to attain maximum strain. The concrete slab specimens were cast and placed in an exposure chamber in which the relative humidity, temperature, and wind velocity were kept at 35 ± 5%, 45 ± 2 °C, and 15 ± 2 km/h, respectively. Results of this investigation indicate that the plastic shrinkage strain varied with the type of superplasticizer and the type of silica fume. Maximum plastic shrinkage strain was measured in the undensified silica fume cement concrete with all superplasticizers. Incompatibility was noted between polycarboxylic ether superplasticizer and plain and two types of silica fume cement concretes.     

异形钢纤维改善混凝土性能研究

采用6种异形钢纤维在体积掺量分别为0.5%、1.0%的情况下,配制CF30、CF50异形钢纤维混凝土,试验结果表明,异形钢纤维混凝土抗折、抗剪和劈拉强度以及弯曲韧性,较基准混凝土有明显提高;干缩值降低,早期塑性开裂也明显减少;不同特征的异形钢纤维改性效果也存在差异。研究发现,《钢纤维混凝土试验方法》(CECS 13∶89)计算纤维混凝土承载能力变化系数的方法有偏差。     

Study of the hydration process of quaternary blended cements and durability of the produced mortars and concretes

This study aims to clarify the effect that blended cements with four components have on the hydration process and durability of concrete. Therefore, blended cements with two different proportions of high calcium fly ash, natural pozzolan and limestone have been produced and have been compared with CEM I. Compressive strength was measured at different ages and the hydration kinetics was studied by means of proton nuclear magnetic resonance (NMR-H). Furthermore, the above mentioned cements have been used to produce mortars and concretes and their durability have been determined. The aspects of durability that has been determined are: pore size distribution by means of NMR-H and mercury intrusion porosimetry, penetration of chlorides, carbonation and resistance to sulfates attack. The conclusion of the present study is that quaternary blended cements can perform as well as CEM I cement as far as compressive strength are concerned and they produce durable mortars and concretes.     

水泥基材料塑性收缩抗裂判据研究

采用自行设计的塑性抗拉强度、塑性收缩开裂应力测定装置测试了水泥砂浆、混凝土塑性抗拉强度和塑性收缩开裂应力.出现塑性收缩开裂时,试件表面实际的塑性收缩开裂应力应大于或至少等于其塑性抗拉强度,据此提出了以试件的毛细管收缩开裂应力临界作用深度来计算其他试件的名义开裂应力,再以此计算它们的塑性收缩开裂抗裂指数,从而得出水泥基材料塑性收缩开裂抗裂判据的思路.实验发现:当抗裂指数≤1.360时,水泥砂浆、混凝土出现塑性收缩开裂;当抗裂指数>1.360时,水泥砂浆、混凝土不出现塑性收缩开裂.     

Production of high strength concrete by use of industrial by-products

Blast furnace slag aggregates (BFSA) were used to produce high-strength concretes (HSC). These concretes were made with total cementitious material content of 460–610 kg/m³. Different water/cement ratios (0.30, 0.35, 0.40, 0.45 and 0.50) were used to carry out 7- and 28-day compressive strength and other properties. Silica fume and a superplasticizer were used to improve BFSA concretes. Slump was kept constant throughout this study. Ten percent silica fume was added as a replacement for ordinary portland cement (OPC) in order to obtain HSC. The silica fume was used as highly effective micro-filler and pozzolanic admixture. Superplasticizer at dosages of 2%, 1.5%, 1%, 0.5% and 0% by OPC weight for 0.30, 0.35, 0.40, 0.45 and 0.50 w/c ratios, respectively, were adopted. Results showed that compressive strength of BFSA concretes were approximately 60–80% higher than traditional (control) concretes for different w/c ratios. These concretes also had low absorption and high splitting tensile strength values. It is concluded that BFSA, in combination with other supplementary cementitious materials, can be utilized in making high strength concretes.     

Experimental investigation on freeze−thaw durability of polymer concrete

Assessing the durability of concrete is of prime importance to provide an adequate service life and reduce the repairing cost of structures. Freeze–thaw is one such test that indicates the ability of concrete to last a long time without a significant loss in its performance. In this study, the freeze–thaw resistance of polymer concrete containing different polymer contents was explored and compared to various conventional cement concretes. Concretes’ fresh and hardened properties were assessed for their workability, air content, and compressive strength. The mass loss, length change, dynamic modulus of elasticity, and residual compressive strength were determined for all types of concretes subjected to freeze–thaw cycles according to ASTM C666-procedure A. Results showed that polymer concrete (PC) specimens prepared with higher dosages of polymer contents possessed better freeze–thaw durability compared to other specimens. This high durability performance of PCs is mainly due to their impermeable microstructures, absence of water in their structure, and the high bond strength between aggregates and a polymer binder. It is also indicated that the performance of high-strength concrete containing air-entraining admixture is comparable with PC having optimum polymer content in terms of residual compressive strength, dynamic modulus of elasticity, mass loss, and length change.