Effects of curing time and temperature on strength development of inorganic polymeric binder based on natural pozzolan

This paper reports the results of a study on the influence of curing conditions on compressive strength development in inorganic polymeric binder prepared from natural pozzolan. Three mixes with different chemical formulations were prepared and cured hydrothermally at different temperatures and times. In particular, the effect of a precuring at an atmosphere of more than 95% relative humidity at room temperature on compressive strength development before the application of heat was studied. Different curing regimes including hydrothermal treatment in steam-saturated atmosphere at different temperatures of 45, 65, 85 °C and for different time periods of 5, 10, 15, and 20 h after 1 and 7 days of precuring were applied. The mix exhibiting the maximum compressive strength after hydrothermal treatment was selected and cured in autoclave at temperatures of 125, 150, 180, and 210 °C for different time periods of 20, 30, 40, and 50 h for investigating the effects of higher times and temperatures of curing on strength development and also to determine the maximum achievable compressive strength. Results show that relatively long precuring in humid atmosphere is very beneficial for compressive strength development. The highest compressive strength achieved for three different regimes of curing including 28 days at an atmosphere of more than 95% relative humidity at 25 °C, 20 h hydrothermal treatment at 85 °C after 1 day precuring, and 20 h hydrothermal treatment at 85 °C after 7 days precuring were 37.5, 37.5, and 57.5 MPa, respectively. The maximum achievable compressive strength under autoclave curing at 210 °C for 30 h after 7 days of precuring was 108.7 MPa.     

Effect of curing time on microstructure and mechanical strength development of alkali activated binders based on vitreous calcium aluminosilicate (VCAS)

The aim of this paper is to study the influence of curing time on the microstructure and mechanical strength development of alkali activated binders based on vitreous calcium aluminosilicate (VCAS). Mechanical strength of alkali activated mortars cured at 65 °C was assessed for different curing times (4–168 h) using 10 molal NaOH solution as alkaline activator. Compressive strength values around 77 MPa after three days of curing at 65 °C were obtained. 1·68 MPa/h compressive strength gain rate was observed in the first 12 h, decreasing to 0·95 MPa/h for the period of 12–72 h. The progress of geopolymeric reaction was monitored by means of TGA and, electrical conductivity and pH measurements in an aqueous suspension. Significant decrease in pH and electrical conductivity were observed in the 4–72 h period, demonstrating the geopolymerization process. Furthermore, SEM images showed an important amount of (N, C)ASH gel and low porosity of the developed matrix.     

Compressive strength and drying shrinkage of fly ash-bottom ash-silica fume multi-blended cement mortars

This paper studies the physical properties, compressive strength and drying shrinkage of multi-blended cement under different curing methods. Fly ash, ground bottom ash and undensified silica fume were used to replace part of cement up to 50% by weight. Specimens were cured in air at ambient temperature, water at 25, 40 and 60 °C, sealed with plastic sheeting for 28 days. The results show that absorption and volume of permeable pore space (voids) of blended cement mortars at 28 day under all curing methods tend to increase with increasing silica fume replacement. The compressive strength of blended cement with fly ash and bottom ash was lower than that of Portland cement control at all curing condition while blended cement with silica fume shows higher compressive strength. In addition, the compressive strength of specimens cured with water increased with increasing curing temperature. The drying shrinkage of all blended cement mortar cured in air was lower than that of Portland cement control while the drying shrinkage of blended cement mortar containing silica fume, cured with plastic sealed and water at 25 °C was higher than Portland cement control due to pore refinement and high autogenous shrinkage. However, the drying shrinkage of blended cement mortar containing SF cured with water at 60 °C was lower than that of Portland cement control due to lower autogenous shrinkage and the reduced microporosity of C–S–H.     

Influence of mix proportions and curing conditions on tensile splitting strength of high strength concretes

The effect of the composition of high strength concretes with low water to binder ratio and silica fume on the development of splitting tensile strength was studied. A statistical approach was employed to develop formulation which could adequately describe the relations between splitting tensile strength and the concrete composition, when cured in two different regimes: water curing at 20°C and sealed curing at 30°C. Autogenous shrinkage was induced in the second type of curing but was largely eliminated in the first one. The relations were presented as nomograms which could be used as a basis for mix design. The correlation between tensile splitting strength and compressive strength could not be described in terms of a simple linear relation with a characteristic constant. For the range of variables studied, the ratio between tensile and compressive strength varied over a large range of 0.08 to 0.12. As a result, the relations developed here for tensile strength are quite different in nature than those for compressive strength in a previous study. Analysis of the data suggest that tensile strength is sensitive to effects which induce autogenous shrinkage to a much greater extent than compressive strength. It is proposed that this may be the main reason for the different trends observed for the relations between the composition of the low water/binder ratio concretes and their compressive and tensile strength.     

Long-term thermal stability of carbon fibre-reinforced addition-type polyimide composite in terms of compressive strength

A previously developed carbon fibre-reinforced addition-type polyimide composite material was exposed to temperatures of 240, 270 and 300 °C in air for 3000 h to study its long-term stability in terms of its compressive strength. The in-plane shear modulus, compressive failure mode and transverse crack density were also evaluated to determine whether a degradation process induces a decrease in the compressive strength of a high-temperature polymer matrix composite having a laminated configuration of [90/0]_4s. The carbon fibre-reinforced polyimide composite exhibited excellent thermal stability in terms of its compressive strength after being subjected to ageing at 240 °C for 3000 h and at 270 °C for 2000 h, with degradation becoming significant at 300 °C. The compressive strength decreased only when the surface degradation caused the 90° plies sandwiching the 0° plies to degrade severely.     

Geopolymerization of a silica residue from waste treatment of chlorosilane production

A silica residue from waste treatment of chlorosilane production was used together with solid sodium aluminate to test its applicability for the production of one-part geopolymers. The blend was activated with water and cured at 70 °C. The degree of reaction and strength were determined after 1, 3, and 7 days. The reaction products were analyzed by XRD and SEM/EDX. Until the third day of curing the degree of reaction of the residue reached 51 % and the strength was 8.9 MPa. The reaction product was identified as geopolymer containing zeolite A. Thus, the results confirmed that the residue may be used in the production of geopolymers. However, after 3 days of curing no further progress of reaction was observed and the strength slightly decreased, which was attributed to changes in the structure of the geopolymeric gel. It was further observed that even harsh vacuum drying left some water (presumably zeolitic water and surface hydroxyl groups) in the geopolymer.     

A novel water permeable geopolymer with high strength and high permeability coefficient derived from fly ash,slag and metakaolin

In this work, a new water permeable geopolymer with high strength and high water permeability coefficient based on fly ash-slag-metakaolin was proposed. The experimental results show that fresh geopolymer composite exhibits dry characteristic and porous structure. The void ratio is 27.6% and the permeability coefficient reaches 1.70 cm/s. The compressive strength and flexural strength reach about 30 MPa and 6.2 MPa, respectively at 1 day and reach as high as 49 MPa and 11.3 MPa at 28 days of curing, respectively. After 100 freeze-thaw cycles, the terminal remaining mass is still larger than 80% along with internal damages and deteriorations on geopolymer paste coating. The dense microstructure of geopolymer matrix and interfacial transition zone indicates the high compressive strength, flexural strength and high freeze-thaw resistance of water permeable geopolymer.     

Isotropical conductive adhesives with very-long silver nanowires as conductive fillers

Isotropical conductive adhesives (ICAs) have garnered great attention from the researchers in electronic industry as a potential substitute to lead-bearing solders for novel microsystem. In this paper, silver nanowires with a diameter of approximately 390 nm and a length of over 100 μm were synthesized by a polyol process. The ICAs composed of an epoxy-based binder containing silver nanowire were prepared and the curing behaviors, electrical properties, hygroscopicity, and the tensile shear strength of ICAs were investigated. Silver nanowires affect the curing behavior of epoxy resin and reduce the cross-linking density. The resistivity of the ICAs filled with 10, 35 and 45 wt% silver nanowire cured at 150 °C is 8.9 × 10^?3, 1.69 × 10^?5 and 4.9 × 10^?6 Ω cm respectively. The resistivity of the ICAs filled with silver nanowire cured at 150 °C is little change after aged under 85 °C/85 % for 264 h. With the increase of the loading of silver nanowire the tensile shear strength of the ICAs increase. The reasons for the effects of silver nanowires on the curing behavior and the electrical property and hygroscopicity and the tensile shear strength were discussed in terms of the morphology, distribution, and higher activity of silver nanowires.     

Creep and drying shrinkage of a blended slag and low calcium fly ash geopolymer Concrete

The main purpose of this research is to study the time dependent behaviour of a geopolymer concrete. The geopolymer binder is composed of 85.2 % of low calcium fly ash and only 14.8 % of ground granulated blast furnace slag. Both drying shrinkage and creep are studied. In addition, different curing conditions at elevated temperature were used. All experimental results were compared to predictions made using the Eurocode 2. The curing regime plays an important role in the magnitude and development of both creep and drying shrinkage of class F fly ash based geopolymer concrete. A minimum of 3 days at 40 °C or 1 day at 80 °C is required to obtain final drying shrinkage strains similar to or less than those adopted by Eurocode 2 for ordinary Portland cement (OPC) concrete. Creep strains were similar or less than those predicted by Eurocode 2 for OPC concrete when the geopolymer concrete was cured for 3 days at 40 °C. After 7 days at 80 °C, creep strains became negligible.     

Microstructural, electrical, and mechanical characterization of Bi2Cu0.1V0.9O5.35 (BICUVOX) ceramics fabricated from co-precipitated precursor powders

Copper-doped bismuth vanadate (Bi₂Cu_0.1V_0.9O_5.35, BICUVOX) was synthesized by a co-precipitation process which resulted in a homogenous, fine-grained powder with an average particle size of ~0.45 μm. The consolidated BICUVOX powder was sintered at temperatures between 625 and 800 °C for 0–8 h in air. The correlation between the thermal processing schedule and the final microstructure were completed for all conditions through stereological analysis of the resultant cross-sectional scanning electron microscope images. From this work, the sintering schedule of 675 °C for 1 h resulted in acquiring a BICUVOX ceramic microstructure that displayed ~97 % relative density with an average grain size of ~1.29 μm. This processing condition was ~75–125 °C lower than typical sintering temperatures for the same density, and resulted in a final grain size that is ~5–10 μm smaller in size. The four-point conductivity testing of the BICUVOX ceramics in air showed values of ~0.003–0.007 and ~0.07–0.12 S/m at 300 °C and 500 °C, respectively, depending upon the thermal processing schedule. The average flexure strength of the same BICUVOX membrane was measured using a ring-on-ring configuration, and this measurement showed flexural strengths as high as 159.3 MPa. This strength is ~92 % greater than previously reported values for BICUVOX membranes.     

Structural behavior of alkali activated fly ash concrete. Part 1: mixture design, material properties and sample fabrication

Alkali Activated Fly Ash Concrete (AAFAC) is an alternative form of concrete that uses fly ash as a 100 % replacement for ordinary portland cement. In producing AAFAC, fly ash is combined with alkali activators that chemically react to form a binder. When combined further with fine and coarse aggregates and often cured at elevated temperature, a concrete material is produced with strength and stiffness properties similar to ordinary portland cement concrete (OPCC). In this paper fabrication of full scale steel reinforced AAFAC beams is presented. The research scope includes: development of an AAFAC mixture design, fabrication of nine AAFAC beam samples, development of an elevated temperature curing system, temperature measurement during curing, and investigation of hardened AAFAC material properties. Results show AAFAC can be manufactured in the same way as OPCC, and that it has a self consolidating consistency in the fresh state. Curing at 60 °C for 24 h produced very rapid strength gain. Compression strengths at 1 day ranged between 47 and 53 MPa, with 28 days compression strengths ranging from 48 to 55 MPa. Material test results show AAFAC is a brittle material with an approximately linear stress–strain response, and an elastic modulus slightly less than that predicted by ACI 318.     

Influence of steam curing on the properties of concretes incorporating metakaolin and silica fume

In this paper, influence of steam curing on the compressive strength, ultrasonic pulse velocity, water sorptivity, chloride ion permeability, and electrical resistivity of metakaolin and silica fume blended concretes were investigated. A total of seven mixtures containing various combinations of Portland cement (PC), silica fume (SF), and metakaolin (MK) were produced with 400 kg/m³ of total cementitious materials content and with a constant water/binder ratio of 0.44. For each mixture, concrete samples were either standard-cured in water at 23°C or steam-cured at 70°C maximum temperature over 17 h curing period. Test results revealed that steam curing enhanced the 1-day compressive strength and ultrasonic pulse velocity while leading to reduced long term strength in line with earlier findings. At the end of the water sorptivity, chloride ion permeability, and electrical resistivity tests, it was found that the steam-cured concretes had higher water sorptivity and chloride ion permeability, and lower electrical resistivity values compared to the standard cured specimens. Use of SF and MK as cementitious materials remarkably decreased the water sorptivity and chloride ion permeability of concretes, irrespective of the curing condition.     

An application of blended fly ash and residual rice husk ash for producing green building bricks

The present study investigates the possibility of using a blended class-F fly ash (FA) and residual rice husk ash (RHA) in the production of green building bricks through the application of densified mixture design algorithm (DMDA) in order to provide a new use for solid waste materials. This study uses unground rice husk ash (URHA) as a partial fine aggregate substitution (10–40%) in the studied cementitious mixtures. Solid bricks of 220 × 105 × 60 mm in size were prepared under forming pressure of 25–35 MPa, a curing temperature of 90 °C, and a relative humidity of 50%, for tests that assessed: compressive strength, flexural strength, bulk density, void volume, and water absorption. The test results showed that all brick samples demonstrated excellent properties. Compressive strength and flexural strength ranged, respectively, between 20.2–33 MPa and 5.4–6.9 MPa. Additionally, up to 30% of URHA content, the values of water absorption and void volume ranged, respectively, between 8.8–15.7% and 1.5–2.1%. All of these values not only conformed well to the requirements of the Vietnamese codes but also demonstrated great potential for using a blended FA–RHA in producing green building bricks.     

Durability of cementitious binder derived from industrial wastes

The durability of cementitious binder hydrated at 27°C and 50°C under high humidity was examined by alternate wetting and drying, as well as heating and cooling, cycles at temperatures ranging from 27°C to 60°C and by performance in water. The results show that cementitious binder hardened at 50°C possesses higher water resistance and lower porosity than the binder hardened at 27°C. A decrease in the strength of the cementitious binder was observed with an increase in temperature and in the wetting and drying and heating and cooling cycles. The maximum decrease in strength occurred at 60°C. The cementitious binder cured at 27°C showed a much smaller decrease in strength with a rise in temperature and in weathering cycles. The changes in strength of the cementitious binder were monitored by differential thermal analysis and microscopy.     

Compressive strength of high strength class C fly ash-based geopolymers with reactive granulated blast furnace slag aggregates designed by Taguchi method

Compressive strength of geopolymeric specimens produced by class C fly ash and granulated blast furnace slag aggregates has been studied. Four different independent factors comprising of aggregate content, sodium hydroxide concentration, curing time and curing temperature were considered as the variables. To attain the maximum possible accurate responses by means of the smallest amount of examinations, Taguchi design of experiment method was followed. By taking into account three levels for each factor, 9 series of experiments were conducted on the specimens at 2 and 7 days of water curing regime. For both considered regimes, a specimen with 30 weight percent of aggregate and sodium hydroxide concentration of 12 M cured at 90 °C for 16 h had the highest compressive strength. On account of reactivity between aggregates and the fly ash, the compressive strength was reached to 69.3 ± 5.3 MPa and 76.2 ± 3.6 MPa at 2 and 7 days of water curing, respectively. Fracture surface of specimens with the highest and the lowest strengths as well as effect of each considered factor on the compressive strength of the specimens were studied.     

Investigation the glazability of dimension andesites with glaze coating materials containing boron minerals in construction sector

This study examined the usability of thin plates cut from rocks of volcanic origin as new decorative indoor and outdoor coating material when used instead of ceramic saddle. The study examined the basic material characterization of andesites and the glazability of andesites with glaze coating materials containing boron minerals. The series of characterization tests were conducted on andesite samples. Then, the samples were applied glaze for trial purposes. Analysis indicated that the andesite samples consisted of sanidine, mica and pyroxene minerals and its apparent porosity, density, water absorption, salt crystallization resistance, compressive strength, frost after compressive strength, bending strength and impact resistance values were 15.75 %, 2,640 kg/m³, 7.41 %, 1.06 %, 47.03 MPa, 45.25 MPa, 10.16 MPa and 9.87 kPa respectively. In heat microscope measurements, maximum sintering was recorded at 1,182 °C. Linear expansion coefficient (α) of the andesite at 400 °C was 4.69 × 10^?6 K^?1. Firing performed by using the prepared glaze recipe at approximately 1,055 and 1,000 °C produced good results in terms of body-glaze harmony.     

Effect of curing parameters on CO2 curing of concrete blocks containing recycled aggregates

In this study, a CO₂ curing process was adopted in order to promote rapid strength development of concrete blocks containing recycled aggregates. The influence of several factors associated with the curing conditions on the curing degree and compressive strength of the concrete blocks were investigated, including curing time, temperature, relative humidity, pressure and post-water curing after the pressurized CO₂ curing (PCC) process. In addition a flow-through CO₂ curing (FCC) method at ambient pressure was also used. The results of the PCC experiments showed that, considerable curing degree and compressive strength were attained during the first 2 h of CO₂ curing, and a prolonged curing time yielded slower gains. The variations of temperature from 20 °C to 80 °C and relative humidity from 50% to 80% had limited impacts on PCC; but the effects of CO₂ gas pressure on the curing degree and compressive strength were more pronounced. The post-water curing after pressurized CO₂ curing allowed the concrete blocks to attain further strength gain but its effectiveness was inversely proportional to the CO₂ curing degree already attained. The FCC experimental results indicated that although a lower curing degree and slower strength development at the early age were observed, after 24 h of curing duration, they were comparable to those obtained by the PCC method. To assess the thermal stability of the concrete blocks, the optimum CO₂ curing regime was adopted for preparing the concrete blocks with recycled aggregates, and the CO₂ cured specimens exhibited better fire resistance than the water-cured ones at 800 °C.     

Fire-resistant geopolymer bricks synthesized from high-calcium fly ash with outdoor heat exposure

This research proposed an alternative utilization of high-calcium fly ash to produce geopolymer bricks for fire-resistant applications. Outdoor heat exposure (OHE) was applied to cure geopolymer mortar. The temperature was up to 40 °C. Geopolymer brick was created with a 30-day compressive strength of 47 MPa via OHE curing for 3 days. The brick experienced a low weight loss after the firing test, which indicated its fire-resistant property. For the flame test, the maximum temperature on the opposite side of the brick from the flame was lower than 380 °C, with no observable cracks, complying with the fire-test requirement. Therefore, high-calcium fly ash geopolymer cured with OHE is suitable for use as a fire-resistant material. In addition, outdoor heat exposure is a promising renewable means to cure geopolymer.     

Mechanical properties of concrete containing phase-change material

This study aimed to investigate the mechanical properties of concrete containing solid–liquid phase-change material (PCM) and focused on two key factors. First, a systematic study on the mechanical performance of PCM-modified concretes was conducted, including compressive, elastic modulus, and shrinkage tests. Second, because PCM provides high latent heat during the solid–liquid phase change, the effects of the solid phase and liquid phase on the mechanical properties of concrete were also explored. Results of this study showed that the solid–liquid phase of PCM affected the mechanical properties of concrete. For example, the compressive strength of 10% PCM concrete in solid phase (23 °C) and liquid phase (40 °C) at 28 days was 29.30 and 19.57 MPa, respectively. In addition, with increasing PCM content, the mechanical properties were degraded. For example, 10, 20, and 30% of PCM content lowered the compressive strength by 35.4, 58.4, and 74.3%, respectively. Therefore, concrete with PCM may not be suitable for structural elements. However, PCM is an important solution for optimizing energy consumption in modern buildings. It can absorb or emit large amounts of heat to store or release thermal energy. These properties can be used to control building temperatures resulting in energy saving and carbon reduction.     

Effects of activator type/concentration and curing temperature on alkali-activated binder based on copper mine tailings

This article investigates the effects of activator type/concentration and curing temperature on alkali-activated binder based on copper mine tailings (MT). Different alkaline activators including sodium hydroxide (NaOH), sodium silicate (SS), and sodium aluminate (SA) at different compositions and concentrations were used and four different curing temperatures, 60, 75, 90, and 120?°C, were considered. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), and X-ray diffraction (XRD) were conducted to investigate the effect of these factors on the unconfined compressive strength (UCS), microstructure, and phase composition of the binder. The results indicate that NaOH concentration and curing temperature are two important factors that affect the UCS and micro-structural properties of the alkali-activated MT binder. The optimum curing temperature, i.e., the curing temperature at the maximum UCS, depends on the NaOH concentration, lower optimum curing temperature at smaller NaOH concentration. Addition of aqueous SS to the NaOH solution can lead to strength improvement, with the highest UCS obtained at a SiO₂/Na₂O ratio of 1.0–1.26. Addition of powder SA to the NaOH solution profoundly delays the setting at 60?°C but improves the UCS at 90?°C. The SEM/EDX results show highly heterogeneous microstructure for the alkali-activated MT binder as evidenced by the variable Si/Al ratios in different phases. The XRD patterns indicate a newly formed crystalline phase, zeolite, in the 90?°C-cured specimens. The results of this study provide useful information for recycling and utilization of copper MT as construction material through the geopolymerization technology.