Effect of mix design inputs,curing and compressive strength on the durability of Na2SO4-activated high volume fly ash concretes

This paper aims to advance research on the use in concrete of a high volume of fly ash, with a high loss on ignition value, aiding in sustainable low carbon footprint construction. To this end, the work explores the benefits that may be achieved in terms of long-term concrete performance from the incorporation of fly ash along with a chemical activator. Durability tests are performed on concrete with an activated hybrid cementitious system: Portland cement (PC) and high volume fly ash with sodium sulfate. The chloride diffusion coefficient significantly decreased over time for the activated system (50% PC - 50% fly ash with added sodium sulfate) compared to the control samples (100% PC and 80% PC - 20% fly ash) at the same water to cementitious material ratio. This behavior is particularly evident in samples cured under controlled laboratory conditions (100% RH and 23 °C). However, outdoor curing increases the permeability for all concretes. Long term carbonation is also investigated under natural exposure conditions, and samples that are cured outdoors exhibit a significant carbonation depth. The compressive strength is correlated with the durability parameters: the durability performance improves as the compressive strength increases, indicating that as is the case for Portland cement (but not always for alkali-activated binders), the microstructural factors which yield high strength are also contributing to durability properties.     

Effect of mineral admixtures and steel fiber volume contents on the behavior of high performance fiber reinforced concrete

High Performance Fiber Reinforced Concrete (HPFRC) is a structural material with advanced mechanical properties. The structural design of HPFRC members is based on the post-cracking residual strength provided by the addition into the mix of the fibers. Moreover, the addition of different types of mineral admixtures influences the overall behavior of this material. In order to optimize the performance of HPFRC in structural members, it is necessary to evaluate the mechanical properties and the post-cracking behavior in a reliable way. As a result, an experimental study on six different sets of HPFRC specimens was carried out. The main parameters that varied were the fiber volume content and the types of mineral addition. The behavior in compression, in flexural tension and the shrinkage properties were evaluated and critically analyzed in order to give a guide for structural use.The results showed that by adding high fiber volume content and the Algerian blast furnace slag into the mix, the HPFRC material obtained has a very good performance and it is suitable for use in practice.     

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.     

Comparative study on strength,sorptivity, and chloride ingress characteristics of air-cured and water-cured concretes modified with metakaolin

This paper reports an investigation in which the performance of plain and metakaolin (MK)-modified concretes were studied under two different curing regimes. The purpose of this study is to evaluate the effectiveness of MK in enhancing the strength and permeation properties of concrete. MK was used to replace 0–20% of Portland cement by weight in concrete with two water-binder (w/b) ratios of 0.35 and 0.55. The change in compressive strength, sorptivity, and chloride ingress with age at all cement replacement levels under both air and water curing are compared with those of the control concrete. The results indicated that the inclusion of MK greatly reduced sorptivity and chloride permeability of concrete in varying magnitudes, depending mainly on replacement level of MK, w/b ratio, curing condition, and chloride exposure period. It was found that under the inadequate or poor curing, MK-modified concretes suffered a more severe loss of compressive strength and permeability-related durability than the plain concretes.     

Effect of granulometry on cementitious properties of ladle furnace slag

Ladle furnace slag (LFS), a by-product of the steel making process, was tested for its potential use as a supplementary cementing material. The material used for the tests was screened or ground, producing three samples of different fineness, and the granulometry of these LFS samples was also tested by particle size analysis. Their chemical and mineralogical composition was assessed by chemical analysis, X-ray diffraction and thermogravimetric analysis. Finally, in order to determine the cementitious and pozzolanic character of LFS in relation to its granulometry, slag-lime and slag-cement mortars were produced and tested in compression. The results show that although LFS is a weak supplementary cementing material, it shows some self-cementing and pozzolanic properties that can be enhanced by screening or grinding the raw material. Even though different levels of fineness and granulometry can be reached with each method, generally, grinding seems to improve LFS binding properties more than sieving.     

A novel conversion of Ti-bearing blast furnace slag into Ti-containing zeolites: Comparison study between FAU and MFI type zeolites

In this work, the synthesis of FAU and MFI type Ti-containing zeolites from Ti-bearing blast furnace slag was first achieved via a facile hydrothermal method. The synthesized zeolites were identified to be Ti-NaX and Ti-NaZSM-5 zeolites, with excellent specific surface area of 663.2 and 325.2 m²/g, respectively. Ti species in the Ti-NaX zeolite contained the framework Ti species and amorphous extraframework Ti species, while the Ti species in Ti-NaZSM-5 zeolite were in the form of the two species of above and another anatase TiO_2. To investigate the potential application of the synthesized zeolites in photocatalysis field, an exploratory study was carried out by degradation of methyl orange under UV irradiation. As demonstrated, the Ti-NaZSM-5 zeolite showed higher photocatalytic performance and was more suitable to be the support of the TiO₂ photocatalyst than the Ti-NaX zeolite. Innovative conversion of TBFS into Ti-containing zeolite materials does provide not only a novel and low-cost approach to waste management, but also a promising material candidate for catalytic oxidation and environmental purification.     

Effects of marble powder and slag on the properties of self compacting mortars

In this study, binary and ternary use of marble powder (MP) and ground granulated blast furnace slag (GGBFS) have been investigated in the production of self compacting mortars (SCMs). The marble powder was obtained as an industrial by-product during sawing, shaping, and polishing of marble. A total of 19 SCM mixtures were proportioned having a constant water-binder ratio of 0.40 and the total binder content of 550 kg/m³. The control mixture contained only portland cement (PC) as the binder while the remaining mixtures incorporated binary and ternary blends of PC, MP, and GGBFS. After mixing, the fresh properties of the SCM were tested for mini-slump flow diameter, mini-V funnel flow time, initial and final setting times, and viscosity. Moreover, compressive strength and ultrasonic pulse velocity of the hardened SCMs were measured. Test results indicated that the inclusion of MP increased the V-funnel flow time, setting times, and viscosity of SCMs whereas decreased the hardened properties. Using GGBFS, on the other hand, decreased the V-funnel flow time and viscosity while increased the setting times of SCMs.     

Influence of curing conditions on properties of high calcium fly ash geopolymer containing Portland cement as additive

This paper investigated the mechanical properties and microstructure of high calcium fly ash geopolymer containing ordinary Portland cement (OPC) as additive with different curing conditions. Fly ash (FA) was replaced with OPC at dosages of 0%, 5%, 10%, and 15% by weight of binders. Setting time and microstructure of geopolymer pastes, and flow, compressive strength, porosity and water absorption of geopolymer mortars were studied. Three curing methods viz., vapour-proof membrane curing, wet curing and temperature curing were used. The results showed that the use of OPC as additive improved the properties of high calcium fly ash geopolymer. The strength increased due to the formation of additional C–S–H and C–A–S–H gel. Curing methods also significantly affected the properties of geopolymers with OPC. Vapour-proof membrane curing and water curing resulted in additional OPC hydration and led to higher compressive strength. The temperature curing resulted in a high early compressive strength development.     

A density functional study of structural and elastic properties of LaN under high pressure

Structural and elastic properties of LaN at normal and high pressures are investigated using ab initio calculations based on full-potential linearized augmented plane wave (FP-LAPW) within both local density approximation (LDA) and generalized gradient approximation (GGA). Our results concerning equilibrium lattice parameter and bulk modulus agree well with the available experimental and previous theoretical findings. The transition pressure from NaCl (B1) to CsCl (B2) phase is found to be 31.05 GPa from LDA, and 42.2 GPa from GGA. To the best of our knowledge, the elastic properties for LaN in the B1 structure in the presence of pressure have never been reported so far. The linear pressure coefficients of elastic constants and their related bulk modulus are determined from the pressure dependence of these parameters. Furthermore, the mechanical stability criteria for LaN in B1 phase are found to be fulfilled at normal conditions.     

碱环境下不同应力水平GFRP筋抗拉性能试验

基于ACI 440.3R-04规定的试验方法,对60 ℃碱环境下应力水平分别为0、25%和45%的玻璃纤维塑料（GFRP）筋的抗拉性能进行了试验研究。试件数量共90根,侵蚀时间分别为3.65、18、36.5、92、183天。采用SEM对腐蚀前后GFRP筋的微观形貌进行了观测,发现碱溶液造成了GFRP筋内部结构致密性的降低,且随着应力水平的增加,其降低愈发明显。在60 ℃碱溶液中侵蚀183天后,应力水平为0和25%的GFRP筋的抗拉强度分别下降了48.81%和55.56%,而弹性模量仅分别下降了5.47%和5.73%,应力水平为45%的GFRP筋则出现了断裂现象。GFRP筋的吸湿试验表明,OH^-离子在GFRP筋中的扩散过程符合Fick定律。在分析了应力水平、侵蚀时间等参数对GFRP筋抗拉性能影响的基础上,基于Fick定律提出了碱环境下带应力GFRP筋抗拉强度的退化模型。     

Effect of Mn on damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloy

The effect of Mn on the damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloys has been studied. The damping vs. strain amplitude spectrum of the studied alloys could be divided into three parts. The strain amplitude weakly dependent part appears again when the microplastic strain occurs at high strain amplitude. The mechanical properties of as-cast Mg–3 wt.%Ni alloy could be improved by the addition of Mn, which is due to the refinement of α-Mg dendrites and solid solution strengthening by Mn. In addition, the corrosion resistance of the alloys could also be improved remarkably by the addition of Mn.