Initial Absorption Rate Research Articles

Wind-driven rainwater penetration through brick veneer with and without surface treatments

Rainwater penetration through building enclosures is a critical factor affecting building performance and durability. Understanding and assessing rainwater penetration and its prevention through the brick veneer and brick wall is crucial to controlling and avoiding moisture-related problems such as fungal growth and damages in interior structural elements. Addition of a layer of clay bricks as a cladding (veneer) to the exposed surface of a building envelope is a common practice in Canada. Though clay brick veneer provides adequate weather resistance for the building, it does not offer complete resistance to wind-driven rainwater penetration unless other measures such as surface treatment or additional layer of cladding is incorporated. Hence, studying the aspects of resistance to water penetration of commonly used cladding systems is of utmost importance. This paper presents outcomes of an experimental study conducted to determine water penetration of brick veneer specimens with two different initial rate of absorption values, two void amounts, and three different surface treatments. The study found that the surface treatment is a viable method for improving the resistance of water penetration inside the building envelope and the plastering was found to be the most effective method. The study also found that the initial rate of absorption and thickness of the bricks affect the water penetration; however, void amount in the brick does not affect much on water leakage of the masonry walls. • This paper presents various options to minimize and stop water penetration into the building envelope. • Three different surface treatments of brick veneer on rainwater penetration were studied. • Surface treatment with plaster is able to completely prevent water penetration. • Between the two water repellent treatments, water-based water repellent showed a better performance. • The paper also presents effect of IRA and void percentage of clay bricks on rainwater penetration.

Influence of firing temperature on the ceramic properties of illite-chlorite-calcitic clays

The influence of firing temperature on the ceramic properties of illite-chlorite-calcitic clays has been investigated. Three samples of the same clay deposit have been selected. Weight loss, dimensional changes, water absorption, bulk density, open porosity, flexural and compressive strengths, initial capillary water absorption rate and thermal conductivity have been determined as a function of firing temperature in the range 900-1200 °C with 1 h of soaking time. The microstructures of the fired samples have been examined by SEM and the phase evolution studied by XRD. The water absorption capacity decreased from ∼ 22% at 900 °C/1 h to a maximum of 12% at 1200 °C/1 h with a maximum linear shrinkage of ∼ 2.7%. The open porosities decreased from ∼ 36% at 900 °C/1 h up to ∼ 20% at 1200 °C/1 h as an effect of progressive sintering with higher densification degree of the ceramic bodies. The flexural strength reached a maximum value of ∼ 34 MPa at 1200 °C/1 h. In contrast, the compressive strengths increased by firing up to a maximum of ∼ 114 MPa at 1200 °C/1 h. The thermal conductivity increased slightly as increasing firing temperature with a maximum value of 0.582 W/m·K in samples fired at 1200 °C/1 h. The Ryshkevitch-Duckworth equation was applied and the results indicated that compressive strength is related linearly with open porosity. A linear correlation was found between thermal conductivity and open porosity. The microstructural evolution by SEM indicated that there is a change of the fired samples at 1100 °C as compared to SEM observations at 900 and 1000 °C. There is an increase of contacts between particles and layered structures associated to dehydroxylated clay minerals (illite and chlorite), quartz particles and pores developed by firing. At 1200 °C/1 h, the microstructures have changed associated to the higher degree of vitrification in the fired sample, with consolidation of the material, interparticle and neck contacts with formation of vitrified bridges. The formation of closed and large open pores of several sizes has been achieved by firing. Small particles were observed as a fine precipitation of crystals in the vitrified structures associated to anorthite, hematite and quartz relicts. This change in microstructure allowed deduce that the compressive strength increased upon firing, with maximum values of this ceramic property at 1200 °C. The ceramic bodies were more sintered by firing and the open porosity decreased progressively. Brickmaking is the main application of these fired illite-chlorite calcitic clays. These clays fired at 900–1100 °C, with 1 h of soaking time, could be applied in the fabrication of clay roofing tiles, tiles and even porous ceramic supports with small variations on shrinkage and porosity, good flexural strengths and high compressive strengths. Samples fired at higher temperatures, 1100 °C/1 h, could be applied as ceramic bricks showing a medium porosity (∼ 20%). They show almost the same bulk density when they are fired at lower temperatures (900 °C). Samples fired at higher temperatures (1150–1200 °C/1 h) could be applied as dark ceramic products. This investigation was interesting because a better knowledge of illite-chlorite-calcitic clays applied as ceramic raw materials has been achieved.

Experimental investigations of CO2 absorption and catalyst-aided CO2 desorption performance of several different amines blending with a promoter

This research presented the new experimental results of the absorption and desorption performance of various single and blended solvents in terms of initial CO2 absorption rate, initial desorption rate for blank solvents and solvents with the aid of HZSM-5 catalyst, and equilibrium CO2 solubility. MEA and PZ are two promoters used to facilitate several individual aqueous single solvents including BEA, AMP, BDEA, and MDEA. In order to check the altered performance of absorption and desorption, the solvents were specified at 2.5 M. The initial desorption rate was evaluated by varying the temperature, weight of the solid catalyst, and initial rich CO2 loading. The experimental results were then taken to compare with the obtained data of the benchmark solution (2.5 M MEA). The comparison results revealed that all the selected blank solvent blends can provide better absorption and desorption performance than the blank benchmark solution. The results also indicated that the performance of catalyst-aided CO2 desorption could be strongly affected by the rich loading and operating temperature. Meaning that the activation of proton donation by HZSM-5 was patently affected by the above two conditions, which eventually affect the CO2 separation from the rich solvent.

Methods for evaluating the technical performance of reclaimed bricks

Reusing deconstructed materials and components can help to decrease the environmental burden of buildings. To safely reuse reclaimed items in new construction, methods are needed to reliably identify the essential technical properties of the deconstructed products. This paper looks at salvaged bricks and examines different indirect test methods to assess their properties. The explored test methods include visual observation, pitch of a sound, ultrasonic pulse velocity (UPV), and thin section. Reclaimed clay bricks and calcium silicate bricks were used in the research. They originated from four different buildings and from different kinds of structures. New bricks of the same kinds were also tested for reference and the properties were compared to the reclaimed ones. The assessed properties entail initial rate of water absorption, water absorption capacity, compressive strength, and freeze-thaw durability. The results show that it is possible to assess the deviation of properties and sort out exceptional bricks from a series with visual observation and pitch of a sound. The deviation of different properties can also be assessed with the help of UPV. A correlation was found between UPV and water absorption, compressive strength and freeze-thaw durability. Lower UPV values mean higher water absorption capacity and vice versa. Compressive strength of bricks is clearly lower when the UPV value is low and higher when the UPV is high. Bricks with lower UPV values (< 1.5 km/s) were also found to be freeze-thaw durable while those with higher UPV values (> 3.0 km/s) were found to be non-durable. Between the mentioned two values, the freeze-thaw durability varied. Thin section was only used to assess freeze-thaw durability and it was found to be unreliable as a method.

Durability properties of copper slag and coal bottom ash based I-shaped geopolymer paver blocks

Geopolymer mortar was prepared with aluminate and silicate-bearing minerals with caustic activators like fly ash (FA), and copper slag (CS). The impression focused on the entire replacement of extensive and energy-intensive Portland cement and traditional natural fine aggregates with coal bottom ash and CS in manufacturing of sustainable geopolymer paving blocks suitable for both rural and urban infrastructure. The designed paver blocks were tested for various durability tests such as water absorption, chemical resistance, abrasion resistance, efflorescence and initial rate of absorption. In overall, the findings indicate the recommendation of geopolymer paving blocks containing 70% of CS and 30% of CBA with different concentrations of alkali activators. Also, the aforesaid geopolymer paver blocks, were found to be efficient compared to conventional (FA and PC) based paver blocks as the same were resulted in reduced water absorption (up to 15%). Similarly GPC mixes, resulted in better resistance (as the same were yielded up to 15% and 70%) against abrasion and chemical attack compared to conventional paver blocks respectively. Based on experimental findings, irrespective of the cost, the designed GPC mixes demonstrated excellent resistance towards aforementioned durability aspects compared to the conventional mix based paver blocks.

Evaluation of test procedures for durability and permeability assessment of concretes containing calcined clay

The durability and permeability of concrete could be investigated by different test methods that evaluate various transport mechanisms of water and ions in cement-based materials. This research has investigated the suitability of conventional permeability and durability assessment test methods for evaluating the properties of concrete mixtures containing calcined clays and limestone calcined clay cements (LC3). The water absorption, capillary water sorptivity, water penetration, surface electrical resistivity, rapid chloride ions migration coefficient, chloride ions’ penetration profile, and diffusion coefficient were examined in concrete mixtures. A rapid approximation method has also been proposed to estimate the kaolinite content of clays based on the chemical composition data. According to the results, water absorption test based on BS 1881-122 could not accurately specify the permeability properties of binary and LC3 blends. Further, the initial rate of capillary water absorption had an appropriate correlation with the results of water penetration and electrical resistivity test methods.

Immobilization of Metals in Fired Clay Brick Incorporated with Aluminium-Rich Electroplating Sludge: Properties and Leaching Analysis

Electroplating sludge is the hazardous waste discarded from the plating and extractive metallurgical process which can only be disposed of at a secured landfill. In this study, the physical and mechanical properties, as well as metal leaching analysis, of fired clay brick incorporated with electroplating sludge (0%, 2%, 4%, 6%, 8% and 10%) were determined. The physical and mechanical properties of bricks, such as firing shrinkage, dry density, initial rate of absorption, water absorption and compressive strength, were tested according to British standard 3921:1985 and British standard EN772:1. Furthermore, the metal leachability was determined by using the toxicity characteristic leaching procedure (TCLP) method 1311. The results show that the utilization of an electroplating-sludge brick up to 4% could enhance physical and mechanical properties, such as reducing the water absorption from 18.3% to 16.1% and increasing the compressive strength from 25.6 MPa to 41.6 MPa. The result also show that 4% of aluminium-rich electroplating sludge incorporated into the brick is the most suitable amount, as it leached less metal concentration and complied with USEPA standards. The metals which were most present in the electroplating sludge (aluminium and iron) drastically reduced from 193,000 ppm to 0.1372 ppm and from 4160 ppm to 0.144 ppm, respectively. Therefore, the electroplating sludge could be fully utilized in the fired clay brick as an alternative to producing low-cost building materials whilst decreasing the levels of disposal of metal sludge on the secured landfill.

Novel rapid-acting sublingual nicotine tablet as a cigarette substitution strategy

Current nicotine replacement products provide a much slower onset of nicotine delivery than cigarettes, and hence are only marginally effective at supplanting cigarette smoking. Therefore, more effective forms of nicotine replacement are needed. This initial investigation characterized the pharmacokinetic (PK) and subjective effects of a novel sublingual (SL) nicotine tablet designed to deliver nicotine more rapidly to the bloodstream of smokers. Study 1 (N = 6) characterized the pharmacokinetics of a 2mg nicotine SL tablet in comparison to an FDA-approved, marketed 2mg nicotine lozenge. Study 2 (N = 24) assessed subjective responses of smokers to a single use of a 1mg and 2mg SL tablet. Study 1 found that the time to maximum blood nicotine concentrations was significantly shorter for the SL tablet (14min) than for the lozenge (82min), and the initial rate of nicotine absorption was higher (0.4ng/mL*min vs. 0.0ng/mL*min), supporting the hypothesis that the SL tablet delivered nicotine more rapidly. Study 2 found that participants reported immediate relief of nicotine withdrawal symptoms after tablet administration, and craving reduction after the 2mg tablet approached the degree reported for their usual brands of cigarettes (4.2 vs. 4.6 on a 7-point scale). Other subjective responses showed the tablet to be an appealing alternative to smoking. The novel SL tablet studied shows promise as a nicotine substitution strategy for tobacco harm reduction and smoking cessation treatment. Additional studies are warranted to further investigate the potential of this new approach.

Effects of hydroxyethyl group on monoethanolamine (MEA) derivatives for biomethane from biogas upgrading

Upgrading of biogas to produce biomethane is an essential way to increase the calorific value of biogas by separating CH4 and CO2 to satisfy the global renewable energy demand. In this study, the efficiency of carbon dioxide (CO2) trapping in aqueous monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), and triethanolamine (TEA) solution during biogas upgrading for biomethane was determined. Effects of hydroxyethyl groups on MEA derivatives were investigated in terms of biogas upgrading and regeneration, CO2 desorption heat, initial CO2 absorption rate and CO2/CH4 selectivity. The duration of upgraded biogas meeting certain European Union (EU) application standards for methane purity during upgrading was reduced by 70, 78 and 200 mins for DGA, DEA and TEA respectively compared to MEA due to the partial substitution of H-bonds by hydroxyethyl groups, and the absorption rate was also reduced, whereas TEA was not suitable for biogas upgrading as it was inefficient for biogas upgrading effect and absorption rate. The calculated results from the Gibbs-Helmholtz equation showed that MEA had the largest CO2 desorption heat (82.47 kJ/mol CO2) and the other MEA derivatives had lower desorption heat than MEA, indicating that MEA consumes more energy in the desorption process. As for the equilibrium partial pressure, all amine solutions absorbed less than 0.4% of the total volume of CH4 and had a high CO2/CH4 selectivity.

Regeneration Process of Ammonia-Absorbed Zirconium Phosphate to Zirconium Phosphate

Zirconium phosphate [Zr(HPO4)2·H2O] absorbs 2 mol(NH3)/mol[Zr(HPO4)2·H2O] with a low equilibrium plateau ammonia concentration of around 1 ppm in water. In this study, in order to investigate the regeneration process of ammonia-absorbed zirconium phosphate [Zr(NH4PO4)2·H2O], Zr(NH4PO4)2·H2O was heat-treated above 353 K under an inert gas. Then, the structures of the heat-treated samples were evaluated using powder X-ray diffraction and thermogravimetry–mass spectrometry measurements. Zr(NH4PO4)2·H2O started to desorb ammonia and the crystal water at 353 K. Then, Zr(NH4PO4)2·H2O was changed to the anhydrous monoammoniate [Zr(NH4PO4)(HPO4)] at 473 K and formed anhydrous zirconium phosphate [Zr(HPO4)2] at 673 K. The anhydrous zirconium phosphate and the anhydrous monoammoniate reabsorbed ammonia in ammonia water. Those initial absorption rates were small compared with Zr(HPO4)2·H2O. The slow kinetics of the anhydrous zirconium phosphate corresponded to the small interlayer distances. The ammonia concentration composition isotherms indicated that the anhydrous zirconium phosphate and anhydrous monoammoniate have a low ammonia equilibrium plateau concentration of around 1 ppm in ammonia water. Zr(NH4PO4)2·H2O is formed from Zr(NH4PO4)(HPO4) by the reabsorption of ammonia and water after 1–10 cycles. We found that zirconium phosphate is an ammonia remover which can be used repeatedly at 473 K.

Manufacturing of Sustainable Untreated Coal Ash Masonry Units for Structural Applications.

Burnt clay bricks are one of the most important building units worldwide, are easy and cheap to make, and are readily available. However, the utilization of fertile clay in the production of burnt clay bricks is also one of the causes of environmental pollution because of the emission of greenhouse gases from industrial kilns during the large-scale burning process. Therefore, there is a need to develop a new class of building units (bricks) incorporating recycled industrial waste, leading toward sustainable construction by a reduction in the environmental overburden. This research aimed to explore the potential of untreated coal ash for the manufacturing of building units (coal ash unburnt bricks). Coal ash unburnt bricks were manufactured at an industrial brick plant by applying a pre-form pressure of 3 MPa and later curing them via water sprinkling in a control shed. Various proportions of coal ash (i.e., 30, 35, 40, 45, 50, and 55%) were employed to investigate the mechanical and durability-related properties of the resulting bricks, then they were compared with conventional burnt clay bricks. Compressive strength, flexural strength, an initial rate of water absorption, efflorescence, microstructural analysis via scanning electron microscopy, and cost analysis were conducted. The results of the compressive strength tests revealed that the compressive strength of coal ash unburnt brick decreased with an increase in the content of coal ash; however, up to a 45% proportion of coal ash, the minimum required compressive strength specified by ASTM C62 and local building codes was satisfied. Furthermore, bricks incorporating up to 45% of coal ash also satisfied the ASTM C62 requirements for water absorption. Coal ash unburnt bricks are lighter in weight owing to their porous developed microstructure. The cost analysis showed that the utilization of untreated, locally available coal ash in brick production leads us on the path toward more economical and sustainable building units.

Application of silica fume in high-volume fly ash self-compacting recycled aggregate concrete

ABSTRACT Recent advancement in construction practices demands the utilisation of construction materials in a sustainable way which promotes the use of industrial by-products as Supplementary Cementitious Materials (SCMs) and alternative aggregates to protect diminishing natural resources. The present study proposed the utilisation of high-volume fly ash in the production of Self-Compacting Concrete (SCC) made with varying proportions of coarse and fine recycled aggregates. Natural Aggregates (NA) of both coarse and fine type in high-volume fly ash SCC were replaced with the respective type of recycled aggregates at the dosage of 0%, 50% and 100% by volume and their hardened state behaviour was studied in terms of compressive strength, chloride ion permeability, initial rate of water absorption, sorptivity coefficient and sulphate resistance. Results of the investigation recommends uses of Silica Fume (SF) at 10% dosages in ternary blends of cement along with high-volume fly ash for the production of SCC at 50% replacement level of both coarse and fine recycled aggregates, without compromising the hardened state properties of concrete.

Effects of Alkyl Groups on Monoethanolamine Derivatives for Biomethane from Biogas Upgrading

Amine scrubbing is one of the key technologies for biogas upgrading to biomethane, which can be used to increase the calorific value of biomethane by separating out CO2 to meet the global demand for renewable energy. In this paper, several monoethanolamine (MEA) derivatives with alkyl groups as variables are screened as sorbents for the biogas upgrading process. The effect of alkyl groups on the efficiency of biogas upgrading, the effectiveness of sorbent regeneration, and the selectivity of CO2/CH4 during biogas upgrading are investigated. The analysis of biogas upgrading experiments with different MEA derivatives shows that methyl and butyl are more favorable for improving CO2 absorption and meeting the biogas upgrading effect of methane purity for a long period of time applicable in some countries, and ethyl is more conducive to the regeneration efficiency of amines. The results of the CO2 desorption heat calculations show that the CO2 desorption heat of ethyl monoethanolamine (EMEA) (66.67 kJ/mol CO2), formed by replacing a hydrogen near the nitrogen with an ethyl group, is significantly lower than those of methyl monoethanolamine (MMEA) (73.04 kJ/mol CO2) and butyl monoethanolamine (BMEA) (73.27 kJ/mol CO2), formed by replacing a hydrogen near the nitrogen with a methyl group and a butyl group, respectively. The CO2 desorption heats were significantly lower than those of MEA (82.12 kJ/mol CO2), suggesting that ethyl can significantly reduce the CO2 desorption heat of the amine compared to other alkyl groups. In the CO2/CH4 selectivity experiments, BMEA showed the fastest initial CO2 absorption rate of 0.83%/s, while dimethyl monoethanolamine (DMMEA) showed the lowest initial CO2 absorption rate of 0.16%/s. All amine solutions showed less than 1% absorption of CH4 and had high CO2/CH4 selectivity.

Strength and durability studies on sustainable eco-friendly green solid blocks

ABSTRACT Masonry blocks are the most common material in the construction industry due to their excellent properties in terms of strength and durability. The present article deals with the innovative Solid Block prepared using fly ash, coal ash, lime, olivine sand, granite powder, and crusher sand. Olivine sand is partially substituted for crusher sand and the properties of the Solid Blocks are studied. The properties of the Solid Block are inferred under various parameters and the results are compared with the Conventional Fly Ash Blocks (CFAB). Scanning electron microscopy(SEM) and Energy Dispersive Spectroscopy(EDS) were used to investigate the microstructural characteristics of olivine sand and Solid Block powder. The Green Solid Blocks (SB) are checked for properties like compressive strength, water absorption, weight density, Initial Rate of Absorption (IRA) and sorptivity properties. The chemical resistance behavior of the green Solid Block samples is evaluated. The properties of the green Solid Blocks are interpreted and the innovative green block are found to be greater compared with conventional fly ash Solid Blocks due to the inclusion of olivine sand, thus promoting a sustainable technology with industrial by products. The compressive strength of the solid block is enhanced up to a 15% utilization of olivine sand; beyond that, the compressive strength is gradually decreased.

Well drilling with combined pressure control

The research deals with the analysis of new technologies for drilling oil and gas wells including the technology of managed pressure drilling (MPD). A consideration is given to the equipment for creating differential pressure in the wellreservoir system, which is supplied by the foreign companies Schlumberger, M-I SWACO, AKROS, etc. The analysis is given to the application of the basic complex of managed pressure drilling equipment, which includes the installation of back-pressure control, nitrogen compressor station, choke manifold, separator, rotary wellhead dock, flare tower with ignition system and hardware and software complex. The article also deals with the implementation options of the managed pressure drilling technology through the use of a sealed circulation system, which simplifies the well flushing scheme and ensures smooth adjustment of the flushing agent pressure at the bottomhole. A viable possibility of the presented basic MPD equipment and the attached software and hardware complex to determine the permissible values of reservoir fracturing pressure and formation pressure is studied in order to monitor the pressure profile in the casing annulus. It has been found that managed pressure drilling as a fundamentally new primary penetration technology for the hydrodynamic conditions of the reservoir allows to perform drilling in the zones with almost any initial absorption rate. That means that we do not stop sinking by boring (i.e. circulation) and do not increase the equivalent pressure on the horizon that depends on the equivalent circulating density. The adjustment involves the approximation of the equivalent pressure on the horizon to the formation pressure. The technological process of managed pressure drilling with the use of the discussed equipment will enable better understanding of the efficiency of this drilling technology by the drilling personnel and contribute to its more conscious application by domestic companies.

Performance of Mechanized Pugged Soil Stabilized Adobe

The soil has been the most abundantly available construction material for use in human society, and it has been considered the primary material for any form of construction. Local availability and ease of handling make it one of the most energy-efficient, cost-effective, and reliable building materials for any structure. The traditional construction technology using soil has been undergoing a considerable change over a while, enhancing its quality and durability as a construction material. It has immense benefits in minimizing the impact of environmental pollution. The paper mainly focuses on comparing the strength of Soil Stabilized Adobe (SSA) (size −230 mm*108 mm*100 mm) prepared by mechanized pugging (using wet mixer grinder) and manual pugging. Compare to manual pugging, the process of mechanized pugging increases the consistency of the soil structure making it a homogenous mixture of clay, silt, sand and stabilizers. The soil considered in the study was red soil containing kaolinite type clay and has been reconstituted for 10% clay by adding M−sand. The different parameters considered in the study were: variation in pugging time (Mechanized Pugging −3min, 6 min, and 9 min and Manual Pugging −10 min and 15 min) and stabilizers (Cement alone (8%), lime alone(8%), and Combination of cement (6%) + lime (3%)). The following tests were conducted on SSA samples to study their performance: dry density, compressive strengths, water absorption and initial rate of absorption. The findings showed that, the SSA made by Mechanized pugging is more advantageous compared to Manual Pugging, as it saves time of pugging, increases the strength and consistency of the soil and reduces water absorption. Additionally, increase in pugging time improves the SSAs quality.

Implementation of an automated dryer with solar collector

This research work consists of the development of an automated sustainable drying system using forced and preheated air to reduce the production time of handmade bricks, so a dryer witha solar collector wasimplemented to take advantage of the energy from solar radiation. A virtualinstrument was developed, which allows to visualize the variables of temperature and humidityinside the drying chamber, additionally a temperature control was implemented, this control allows the system to maintain a constant temperature during the drying process. Samples were taken from the production of the brick kiln “El Tejar” and dried by this device, thenthe drying times and their physical and mechanical properties were compared, finding that the bricks dried with the proposed prototype retained these properties. As for the compressive strength tests for samples of both processes was around 30.6 Kgf/cm2 and 31.2 Kgf/cm2, the deflection resistance was around 1.2 Kgf/cm2 and 1.3 Kgf/cm2, the initial absorption rate was around 0.3 g/cm2/min and 0.4 g/cm2/min, and finally the percentage of water absorption for both processes were around 12.9% and 13.1%. The difference lies in the drying times, since drying in the artisanal brick kilns takes about 15 daysin the proposed dryer takes 9 days, resulting in a decrease of 40% in this process.

Influence of off-spec fly ash and surfactant-coated nano-iron-oxide on the fresh and hardened properties of cement pastes: An exploratory study

Millions of tons of Fly Ash (FA) is generated worldwide each year, and this generation is anticipated to grow alarmingly. Despite the application of FA in cement composites and other soil stabilizers, more than 30% of the total FA is considered off-spec and is landfilled, causing different environmental, economic, and health problems. Owing to the scantly available literature and knowledge gap related to incorporating the off-spec FA in cement composites, limited mass applications of off-spec FA have been reported so far. This study aims to investigate the influence of the off-spec FA and surfactant-coated nano-iron-oxide (SNI) solution on the fresh and hardened properties of cement pastes. For this reason, fresh-state flow percentage, setting time, capillary water absorption rate, compressive strength development, pozzolanic activity, and chemical durability (in acid solutions) were compared among the cement pastes containing 40% off-spec FA with and without an SNI addition (0%–3%). Results showed that the SNI addition enhanced workability, compensating for the negative effect caused by the off-spec FA substitution. SNI addition also retarded the initial rate of capillary water absorption and improved the acid resistance of hardened cement paste. Furthermore, slow development of compressive strength of cement pastes is observed by the off-spec FA substitution. Thermogravimetric analysis revealed that the SNI addition made the lesser formation of C–S–H gel and CH at early ages, resulting in a delayed pozzolanic activity. The development of advanced cement composites using off-spec FA and SNI may be a positive step towards an efficient and eco-friendly consumption of industrial wastes in construction materials.

Effect of compression casting technique on the water absorption properties of concrete made using 100% recycled aggregates

Effect of compression casting technique on the water absorption characteristics of low grade 100% Recycled Aggregate Concrete (RAC) of target strength range 11 to 15 MPa to be used in the manufacturing of masonry units is investigated. Water absorption characteristics were determined by performing sorptivity test. Recycled aggregates were produced by crushing laboratory-tested concrete samples of strength ranging from 21 MPa to 28 MPa. Two different ratios of recycled coarse aggregate and recycled fine aggregates were investigated using two different cement contents. For comparison, natural aggregate concrete mixes were also tested. The study parameter included effect of aggregates type, casting pressure, casting technique and cement content on the water absorption properties of RAC. Further, depth of penetration of salt was observed using silver nitrate solution after 3-month immersion in 10% NaCl solution. The results of sorptivity test showed positive impact of compression casting technique on water absorption properties of low grade 100% RAC. Further, results showed that RAC mixes exhibited inferior water absorption properties compared to natural aggregates concrete mixes. Various equations were proposed to predict water absorption of 100% RAC under different conditions of casting pressure and cement content based on initial and secondary rate of water absorption.

Engineering properties of waste-based alkali activated concrete brick containing low calcium fly ash and rice husk ash: A comparison with traditional Portland cement concrete brick

Alkali activated concrete bricks manufactured from waste materials are an alternative to replace PC as the principal binder in brick manufacture. The current study reports the mechanical and durability properties of blended fly ash and 20% rice husk ash (20RHA) alkali activated bricks and compares with Portland cement (PC) bricks (100PC). The 20RHA brick showed a compressive strength growth rate of 4% between 7 and 28 days as compared to 13.8% for 100PC bricks. Both achieved similar 28 days compressive strength (approximately 17 MPa). High tensile strength was observed in 20RHA this is attributed to the high bond strength at the interface of the 20RHA alkali activated binder and aggregates. In microstructural investigation, 20RHA brick displayed a stronger bond within the interfacial transition zone (ITZ) boundary compared to 100PC bricks at all ages. This makes the fracture plane more prone to pass through the aggregates than through the bond interface. Lower capillary suction near the surface for 20RHA concrete is hypothesized as the reason for the lower initial rate of absorption obtained for 20RHA when compared with 100PC. The addition of RHA makes the bricks more vulnerable to efflorescence when exposed to moisture due to the combined effect of the high porosity, a high Na2O/Al2O3 ratio and greater leaching of sodium ions.