Sole Binder Research Articles

A Review of Durability and Strength Characteristics of Alkali-Activated Slag Concrete.

Alkali-activated slag (AAS) is a promising alternative to ordinary Portland cement (OPC) as sole binder for reinforced concrete structures. OPC is reportedly responsible for over 5% of the global CO2 emission. In addition, slag is an industrial by-product that must be land-filled if not re-used. Therefore, it has been studied by many investigators as environmentally friendly replacement of OPC. In addition to recycling, AAS offers favorable properties to concrete such as rapid development of compressive strength and high resistance to sulfate attack. Some of the potential shortcomings of AAS include high shrinkage, short setting time, and high rate of carbonation. Using ground granulated blast furnace slag (GGBS) as an alternative to OPC requires its activation with high alkalinity compounds such as sodium hydroxide (NaOH), sodium sulfate (Na2SO3), sodium carbonate (Na2CO3), or combination of these compounds such as NaOH and Na2SO3. The mechanism of alkali-activation is still not fully understood and further research is required. This paper overviews the properties, advantages, and potential shortcomings of AAS concrete.

Effects of layer-interface properties on mechanical performance of concrete elements produced by extrusion-based 3D-printing

Interfaces between layers in 3D-printed elements produced by extrusion-based material deposition were investigated on both macro- and micro-scales. On the macro-scale, compression and flexural tests were performed on two 3D-printable cement-based compositions (3PCs), namely Mixtures C1 (with Portland cement as sole binder) and C2 (containing pozzolanic additives) at testing ages of 1 day and 28 days. The influences of binder composition and time interval between layers on layer-interface strength were critically analyzed. The investigated time intervals were 2 min, 10 min and 1 day. The investigations revealed that Mixture C2 exhibited lower degrees of anisotropy and heterogeneity as well as superior mechanical performance in comparison to Mixture 1. In particular, Mixture C2 showed a less pronounced (below 25%) decrease in interface bond strength as observed in flexural tests for all time intervals under investigation. In contrast, the decrease in flexural strength measured for C1 specimens amounted to over 90% due to the higher porosity at the interfaces of the printed concrete layers. Microscopic observations supported the findings of the macroscopic investigations. SEM images also delivered additional information on morphology of interfacial defects as well as “self-healing”.

Effect of mix design parameters on mechanical and durability properties of alkali activated slag concrete

This paper evaluates the mechanical and durability performance of Alkali Activated Slag Concrete (AASC) prepared using ground granulated blast furnace slag as the sole binder material. The influence of sodium hydroxide concentration (1 M and 8 M), binder content (300 kg/m3 and 450 kg/m3) and alkaline solution/binder ratio (0.4 and 0.55) on the mechanical and durability properties of alkali activated slag concrete (AASC) were reported. Various tests were carried out to evaluate the durability performance of AASC, which includes sorptivity, acid attack (up to 56 days) due to sulfates, chlorides and nitrates. The concentration of acids was maintained at 5%. The obtained results indicated that the activator concentration has a larger influence on the mechanical strength of AASC followed by alkaline solution/binder ratio. Sorptivity of AASC is significantly affected by activator concentration. Results from acid attack test and XRD indicated a good durability of AASC.

Effect of silicate modulus on the setting, mechanical strength and microstructure of iron-rich aluminosilicate (laterite) based-geopolymer cured at room temperature

This paper studies the alkali activation of iron-rich aluminosilicates (laterites). Three activating alkaline solutions were prepared from sodium hydroxide solution (8, 10 and 12 M) with sodium silicate (Na2SiO3) in order to obtain the sodium silicate solutions with moduli of SiO2/Na2O equal to 0.75, 0.92 and 1.04; H2O/Na2O = 9.78, 10.45 and 12.04. The effects of above-defined solutions on the setting time, physical and microstructural properties of geopolymer binders from calcined laterite (600 °C), containing metakaolinite, as the sole binder at room temperature are reported and discussed. A laterite from Eloumden and one from Odza were used. The synthesized products were labelled GPEL(i=1.04, 0.92 and 0.75) and GPOD(i=1.04, 0.92 and 0.75) series. The dry compressive strength measured after 7 and 28 days were 4–10 and 10–18 MPa, respectively. It was typically found that the geopolymer paste from sodium hydroxide with molar concentration 12 M and the molar ratio SiO2/Na2O of the silicate solution equal to 0.75 produced the highest compressive strength (~ 18 MPa). These samples also have a denser matrix. The dry bulk densities of both series increased with the decrease of silica moduli and were in the range 2.31–2.43 and 2.32–2.52 g/cm3 and the water absorptions were in the range of 8.21–11.40% and 7.23–13.03% for geopolymers GPEL and GPOD series, respectively. The setting time decreased with increasing molarity of NaOH solutions. The physicochemical properties and the mineralogy of both iron-rich aluminosilicates were influenced by the silicate modulus of activating solutions and the best compositions were achieved with characteristic SiO2/Na2O = 0.75 and H2O/Na2O = 9.78.

A Study on the Phosphate-Bonded High-Alumina Castable — Effect of MgO Addition

Mono-aluminium phosphate [MAP, Al(H2PO4)3] is a widely used chemical binder in the refractory industries due to its higher water solubility and greater bonding strength at low temperatures as it reacts with both basic and amphoteric oxides and has higher application temperature. In the present work, commercial-grade MAP is used in high-alumina castables, with different particle size distributions, as the sole binder. The effect of addition of 1 mass-% MgO as a setting accelerator to the castable compositions is also studied. Castables are processed as per conventional processing methods and heat treated after drying at 1000 and 1600 °C. Dried and fired compositions were evaluated for density and strength. Also micro-structural study of the 1600 °C sintered samples was carried out. Addition of MgO resulted in a marginal decrease in density values which may be due to a greater amount of hydrated phase formation and their decomposition at higher temperatures; but it significantly increased crushing strength for all the heat treatment temperatures. Greater bonding from faster reaction at low temperature and the formation of a liquid phase at higher temperatures are the reasons for such an enhancement.

Graphene Oxide-Modified Pervious Concrete with Fly Ash as the Sole Binder

In this study, a graphene oxide modified pervious concrete was developed by using a low-reactivity, high-calcium fly ash as sole binder, chemical activators and other admixtures. The density, void ratio, mechanical strength, infiltration rate, Young’s modulus, and degradation resistance of pervious concrete were measured against other three controlled groups. The test results indicated that the graphene oxide modified fly ash pervious concrete is comparable to the Portland cement pervious concrete. While the addition of 0.03% graphene oxide (by weight of fly ash) increased the compressive strength, split tensile strength, Young’s modulus and degradation resistance of fly ash pervious concrete noticeably, the void ratio and infiltration rate were reduced.

The agglomeration of coal fines using wet microalgae biomass

South African coal generally contains a high percentage of non-carbon mineral matter, which necessitates processing to remove the bulk of the non-carbon material. Such processing results in the formation of some 60 million tons of discard coal and between four and eight million tons of very fine, unusable coal, called ultra-fines, each year. The objective of this study was to investigate factors that impact on the agglomeration of fine coal of <150 mm when using microalgae biomass as the sole binder. Mixtures of coal and wet microalgae biomass were prepared and pelletised. The proximate properties of the mixtures and coal were determined and the physical properties of the pellets measured, such as compression strength, water resistance and impact resistance. The results showed that pelletisation of Coalgae® is a promising technology for the recovery of coal fines. Moisture content, pressure and holding time influence the quality of the pellets. Compression resistance testing indicated that pellets made from the coal80%-algae20% (by weight) mixture were stronger than those made from the coal90%-algae10% (by weight) mixture. Pellets made from samples with ± 17% moisture content exhibited the strongest resistance, one of 1.8 kg/mm2 for the coal80%-algae20% mixture that was centrifuged after 24 hours. The water resistance index for all the pellets was lower than the recommended 95%, which was considered to put emphasis on handling, transportation and storage of the pellets.

Impact in Mineralogical Composition of Geopolymeriz ation Actuation using Fly Ash as the Sole Binder

Impact in Mineralogical Composition of Geopolymeriz ation Actuation using Fly Ash as the Sole Binder

ECG signal compression using parallel and cascade method for QRS complex

Objective: To nullify the use of temperature curing in Self Compacted Geopolymer Concrete (SCGC). Methods/Analysis: SCGC is developed by activating Ground Granulated Blast Furnace Slag (GGBFS). The workability and compressive strength was studied by varying Sodium Hydroxide molarity from 8M to 12 M. Sodium Silicate and Sodium Hydroxide were used for alkaline solution. The water to geopolymer solid ratio was kept 0.25 for all mixes and the total powder content was 500 kg/m3 . The test specimens were cured at 600 C, 700 C, and at ambient temperature to study the effect of temperature on hardened properties. Findings: SCGC satisfied all workability criteria as per the EFNARC guideline. Results show that SCGC with 12M NaOH molarity produced maximum compressive strength. The SCGC specimen cured at 700 C produced the highest hardened properties as compare to 600 C and ambient temperature. As per results, SCGC can be developed at ambient temperature by using GGBFS as a sole binder. Novelty/Improvement: GGBFS enhances early age strength properties and the strength is comparable to heat cured SCGC as well as SCC based on OPC. Keywords: Alkaline Solution, Ambient Curing Temperature, Silicon Dioxide, Sodium Hydroxide, Sodium Silicate

High alumina castables: a comparison among various sol-gel bonding systems

A comparison among various sol-gel bonding systems has been done for high alumina castable refractory. Four different sol systems, namely, alumina, boehmite, mullite, and spinel, have been synthesized and used individually as sole binder in high alumina castable system with particle size distribution coefficient of 0.23 as per Dinger and Funk model. The castable compositions were processed conventionally and properties were evaluated after heat treatment at different temperatures. These developed sol-containing compositions were also compared against commercially available silica sol-containing composition prepared under exactly similar conditions. Mullite sol-bonded composition showed higher cold strength, whereas spinel sol resulted in better hot properties. Improved thermal shock resistance against commercial sol binder was observed in spinel and mullite sol-containing compositions, which may be associated with the microcracking effect produced from the thermal expansion mismatch. The slag corrosion resistance was also observed better for the spinel sol-containing composition. The commercial silica sol-bonded compositions showed higher strength due to its higher solid content but resulted in inferior hot and corrosion properties.

Graphene Oxide Modified Pervious Concrete with Fly Ash as Sole Binder

In this study, a graphene oxide modified pervious concrete was developed by using a low-reactivity, high-calcium fly ash as sole binder, chemical activators and other admixtures. The density, void ratio, mechanical strength, infiltration rate, Young’s modulus, and degradation resistance of pervious concrete were measured against other three controlled groups. The test results indicated that the graphene oxide modified fly ash pervious concrete is comparable to the Portland cement pervious concrete. While the addition of 0.03% graphene oxide (by weight of fly ash) increased the compressive strength, split tensile strength, Young’s modulus and degradation resistance of fly ash pervious concrete noticeably, the void ratio and infiltration rate were reduced.

Natural weathering performance and the effect of light stabilizers in water-based coating formulations on resin-modified and dye-stained beech-wood

This study assesses the performance of untreated and resin-modified beech-wood (Fagus sylvatica L.) during outdoor weathering. Boards modified with thermosetting N-methylol melamine (NMM) and phenol–formaldehyde (PF) resins, which were partly dye stained, were coated solely with a waterborne acrylic binder and formulations containing the same binder with different types and contents of photo-protective additives. Most modifications of the wood substrate changed the original color of wood, except for sole NMM modification. Changes in mass and capillary water uptake during exposure of modified, uncoated and coated boards were less than those of respective controls. Surface defects and cracks were clearly fewer on modified wood than on the controls, but no clear difference was observed among the topcoats containing UV-protective agents (UV-PA). The color stability during outside weathering depended on the treatment and coating formulation. Untreated and NMM-modified boards became grayer, and the NMM-dye-modified boards turned to a lighter gray, while PF-modified boards adopted a darker, blackish color. The weathered coating on the modified boards, particularly with PF resin, showed less blistering, flaking, and cracking than that on the controls. UV-PA stabilized the color and adhesion on all boards compared to the sole binder formulation. We conclude that wood modification with NMM and PF resin improves the natural weathering performance of wood coated with acrylic coatings. Combination of modification with staining enables diversification of the optical appearance.

Development of spinel sol bonded high pure alumina castable composition

A cement free high pure alumina castable composition is developed for high temperature applications using synthesized Mg-Al spinel sol as binder. The spinel sol is prepared from nitrate precursors and characterized for its pH, solid content, particle size, FTIR, thermal behavior (DSC-TG), phase formation with temperature (XRD), microstructure (FESEM), etc. High alumina castable formulations with different particle size distributions (PSDS) are conventionally processed using the synthesized sol as sole binder at two different amounts. Castables were characterized for various refractory properties after heat treatment at different temperatures. The hot strength and the corrosion resistance of the best composition are evaluated and the properties are compared with silica sol bonded high alumina castable with similar formulations, processed under similar conditions. Considerable improvement in terms of hot strength, corrosion resistance and thermal shock resistance are obtained for the spinel sol bonded composition.

Production of cement-free construction blocks from industry wastes

This study explores the possibility of making carbon-negative and cement-free construction blocks using steel slag as sole binder and blast furnace slag as lightweight aggregates through carbonation activation. Both steel slag and blast furnace slag are by-products of steel making process. The goal of the study is to develop a clean production that can utilize slag and carbon dioxide to produce environment friendly construction products. Carbonation activation was implemented during the curing of the blocks to accelerate early strength gain. The physical and durability of slag-bond concrete blocks were examined through their density, water absorption, compressive strength and freeze and thaw resistance. An economic analysis was performed and a carbon balance was computed to evaluate the feasibility of making carbon-negative and economically-competitive slag-bond blocks. This study demonstrates that the proposed process consumes no natural resources, produces no wastes, is capable for carbon sequestration and is a clean production. The slag-bond concrete block is a carbon-negative product. In addition, slag-bond concrete block exhibited better mechanical and durability properties compared to the commercial cement block. The cost analysis suggests that slag-bond concrete blocks can be made at a lower cost compared to the commercial cement block if they are mass produced.

Nano mullite bonded refractory castable composition for high temperature applications

Development of high pure alumina castable is studied by using synthesized mullite sol as the sole binder. Mullite sol is prepared by wet chemical route and is characterized by its solid content, particle size, thermal analysis, phase development with temperature, microstructure, etc. This sol is used at two different percentages in high alumina castable compositions with two different particle size distribution patterns. Conventional castable processing is done on the compositions and the characterizations are done after heat treatment at three different temperatures. Finally, the best composition is also compared with the commercially available silica sol containing high alumina castable with similar particle size distribution. Considerably improved hot strength, high corrosion resistance and flexural strength (hot modulus of rupture) are obtained for the mullite sol containing composition but with relatively lower thermal shock resistance.

Comparison indices for design and proportioning of concrete mixtures taking environmental impacts into account

As awareness and concern for greenhouse gas emissions grow, methods for reducing a significant industrial emission source, the production of cement for use in concrete, have been appearing. Assessments of these methods typically do not take into account the influence of material properties and environmental impacts concurrently. When both are considered, rarely are properties considered other than concrete strength. In this research, methods for assessing environmental impacts with mechanical properties concurrently for design of non-reinforced concrete are presented. Tools for assessing environmental impacts based on the volume of material needed as defined by several material properties and design parameters, such as required moment of inertia and cross-sectional area, are investigated. The indices for comparison developed in this research are applied to a database containing 190 concrete mixtures with varying constituents both with and without Supplementary Cementitious Materials (SCMs). For the mixtures and comparison indices examined, concrete mixtures containing SCMs consistently offered the best combination of associated global warming potential (GWP) and material properties. However, for several cases, it was shown that the use of Portland cement as the sole binder could provide comparable indices of GWP and material properties to concrete mixtures containing replacement binder.

Alkali-activated concrete: Engineering properties and stress–strain behavior

This paper presents an investigation into the tensile strength, modulus of elasticity, Poisson’s ratio, and stress–strain relationships of alkali-activated portland-cement-free concrete made with fly ash or ground granulated blast furnace slag (GGBFS) as the sole binder. Alkali-activated concrete is shown to be stronger in tension and have lower Poisson’s ratio than portland cement concrete. Relationships are proposed to estimate the tensile strength and modulus of elasticity based on the compressive strength of alkali-activated concrete, which are of the same form as those currently employed for portland cement concrete.

The Strength of Alkali-activated Slag/fly Ash Mortar Blends at Ambient Temperature

The implementation of sustainable development in civil engineering society has led to the use of new materials with low environmental impact. Ordinary Portland cement (OPC) is the primary material in the production of traditional concrete. However, the manufacturing of OPC has led to environmental concerns over the production of CO2. The use of fly ash and slag, the most commonly used industrial by-products, as replacements for PC, has helped to reduce these CO2 emission. Recent research has also shown that it is possible to use fly ash or slag as a sole binder in concrete by activating them with alkali components through a polymerization process. However, the main issue of the use of fly ash as a replacement material for cement is the need of heat curing regime to achieve structural integrity. While, the standard curing regime used for OPC concrete can be applied to the alkali-activated slag (AAS) due to the similar characteristic of the hydration product.This paper reports the detail of the experimental work that has been undertaken to investigate the strength of AAS/fly ash (AASF) mortar blends. The AASF specimens were prepared using a mix of ground granulated blast-furnace slag (GGBS) and low calcium class F fly ash activated by high alkaline solution. The mix compositions of slag to fly ash were 1:0, 0.9:0.1, 0.8:0.2, 0.7:0.3, 0.6:0.4 and 0.5:0.5, respectively. The standard curing regime at ambient temperature was applied.The results showed that the mix proportion of 0.5 slag: 0.5 fly ash produced the best strength results. The standard deviation values also reduced along with the increase of fly ash content indicating an improved stability of the specimens. It also suggested that 0.5 slag: 0.5 fly ash blend could provide a solution for the need of heat curing for fly ash-based geopolymer.

Synthesis and Characterization of Alumina Sol and Its Use as Binder in No Cement High‐Alumina Refractory Castables

Alumina sol was prepared from inorganic precursors and characterized for its solid content, particle size analysis, DSC‐TG, phase formation on calcination, etc. The sol was used as sole binder in high‐alumina refractory castables, with different particle size distributions (PSDs), by varying distribution coefficients as per Dinger and Funk model. The castables were processed conventionally and characterized for physical and mechanical properties after heat treatment at various temperatures. Reasonable strength was obtained for the sintered castables, and no impurity phase was found in the matrix phase of the castables.

Special Issue on Sustainable Building Structures

Special Issue on Sustainable Building Structures