Pre-wetting Time Research Articles

Experimental Investigation into Lightweight High Strength Concrete with Shale and Clay Ceramsite for Offshore Structures

To develop lightweight high-strength concrete (LWHSC) for offshore structures in a harsh seawater environment, LWHSC with shale and clay ceramsites was designed. LWHSC was experimentally investigated in terms of density, compressive strength, and durability in a coastal environment. Then, its feasibility for offshore structures was also assessed. The results show that the compressive strength and oven dry density of LWHSC appropriately improve with increases in cement content, while they are reduced by the replacement of shale ceramsite with clay ceramsite. The compressive strength of LWHSC also increases first and then decreases with an increase in the pre-wetting of shale and clay ceramsites. Their optional pre-wetting time is about 0.5 h. LWHSC exhibits a higher brittleness compared with conventional concrete. LWHSC has increases in the resistances of freeze–thaw, carbonization, water penetration, and chloride penetration when the shale and clay ceramsite light aggregates decrease in the concrete. The LWHSC prepared in this paper is suitable for the harsh seawater environment of offshore oil platforms but is limited to the southern region where there is no requirement for the freeze–thaw resistance of concrete. The results of this study can provide some reference for the application of LWHSC in offshore structures and other similar aspects of engineering.

High-performance artificial aggregate prepared with recycled concrete powder and its impact on concrete properties

Given the pollution of waste concrete powder, low utilization rate, sand and stone resources shortage, and poor performance of artificial aggregate, the high-performance artificial aggregate was prepared by high dosage recycled concrete powder (RCP). The effects of curing methods, RCP grinding time, RCP:slag ratio, Na2O dosage, and Na2SiO3 modulus on the properties of the aggregate were studied. The results show that natural curing is the most effective, and the best-performing aggregate was obtained with an RCP grinding time of 40 min. The particle size coefficient of the aggregate was around 1.3, and increasing the proportion of slag increased the content of large particles. The amounts of slag and Na2O had a significant impact on the aggregate. As the amounts of slag and Na2O increased, the amount of C-(A)-S-H gel increased, the microstructure improved, and the macroscopic manifestations increased apparent density and strength and reduced water absorption. The maximum strength of the aggregate reached 8.59 MPa, and water absorption was 12.67% at this point. Concrete was prepared using the aggregate above, and the effects of aggregate curing time, aggregate pre-wetting time, and aggregate material ratios on the properties of the concrete were studied. The results show that the density of RCP artificial aggregate concrete is low, between 2030 kg/m3-2220 kg/m3. The compressive strength and splitting tensile strength of concrete increase with the increase of aggregate curing time, prewetting time, and the dosage of aggregate Slag and Na2O, which reach 59 MPa and 4.5 MPa, respectively. The aggregate strength increased, leading to interfacial failure inside the concrete, while larger aggregate particle size tended to cause aggregate failure inside the concrete.

Study on the Influence of the Pre-Wetting Time of Ceramsite and the Floating Beads Content on the Property of Lightweight High-Strength Concrete

The influence of different ceramsite pre-wetting time and the floating beads content on the properties of lightweight high-strength concrete was studied in this paper. The results showed that as the pre-wetting time increased, the absorption rate of ceramsite continued to increase, reaching a saturated state at 12 h with 36.14% water absorption rate; the concrete slump/expansion degree is increased significantly, and the growth rate decreased gradually, and the improvement was not obvious after 12 h; the 7 d strength of concrete saw an obvious downturn, and the strength dropped by 10.4% at 12 h, after which the decline was basically stable; the 28 d strength, 28 d strength growth rate and 7 d-28 d strength growth rate all showed a steady upward trend, which reached 61.18 MPa, 12.4% and 29.73% respectively at 12 h, and the growth rate was basically stable afterwards; as the floating beads content increased, the concrete dry density, slump/expansion degree, 7 d and 28 d strength all showed a significant decline trend.

The bridging action of microbubbles in particle-bubble adhesion

Microbubbles play an important role in the adhesion between particle and bubble. In this paper, the bridging action of microbubbles on the adhesion between particle and bubble was studied at different pre-wetting times in the sodium oleate system. Many microbubbles formed on coal surface when the coal particles wetted by water. The coal-microbubble flocs were formed through the bridging action of microbubbles. The coal-microbubble flocs attached to the floating bubble increased the adhesion efficiency between bubble and particle because the process of coal-bubble adhesion was converted to the process of coal flocs-bubble adhesion. When the pre-wetting time increased, the number of microbubbles on coal surface decreased, resulting in the decrease of coal-microbubble flocs, which finally reduced the froth product yield of flotation. Additionally, an evaluation index (particle carrying index, PCI) was proposed to assess particle-bubble collection efficiency and the PCI values were positively correlated with the yield of froth products.

Use of recycled fine clay brick aggregate as internal curing agent for low water to cement ratio mortar

This paper investigates the feasibility of using recycled fine clay brick aggregate (RFCBA) for the purpose of internal curing and reducing drying shrinkage of mortar. Effects of RFCBA on fresh and hardened properties of mortar were studied. RFCBA was used to replace river sand (in replacement of 30%, 60%, and 100%, respectively) in making the mortar mixes. Besides, the influence of moisture content of the RFCBA was evaluated by varying its pre-wetting time (0, 30 min, 24 h) before the mix preparation. The experimental results show that the initial slump flow decreases with the increasing RFCBA content and pre-wetting time, while an opposite trend is observed for the slum flow loss. The compressive strength and flexural strength of the RFCBA-mortar decrease with an increase in RFCBA content. The reduction of internal relative humidity can be significantly delayed by the RFCBA. Furthermore, the resistance to drying shrinkage of the RFCBA-mortar mixes improves when the RFCBA content increases due to the releasing of the pre-stored water in the porous RFCBA.

Shrinkage and Strength Properties of Coal Gangue Ceramsite Lightweight Aggregate Concrete

It is a promising and effective method for waste treatment by using coal gangue to make lightweight aggregate concrete. However, lightweight aggregate concrete with low‐density coal gangue ceramsite is prone to cracking during volume shrinkage, which limits its application in the construction industry. In an attempt to resolve the problem of cracking in shrinkage, this study investigated the effect of prewetting time and shrinkage reducing agents on shrinkage volume and concrete strength through a series of concrete shrinkage and strength tests. The experimental results show that shrinkage volume reduced at a prewetting time of 12 hrs or with a 2% addition of D‐230 polyether amine reductant. With the optimal conditions of 12 hrs prewetting time and 2% addition of the reductant, the concrete shrinkage volume significantly decreased with a negligible impact on its strength. Appropriate amount of shrinkage reducing agent and adjustment of prewetting time of coal gangue ceramsite are necessary to reduce the shrinkage rate and improve the stability of the specimen. This is of great significance to wide application of lightweight aggregate concrete with coal gangue ceramsite.

Effects of pre-wetting time on surface topography and floatability of lignite particles

The laser particle size analyzer, NMR, SEM/EDS, induction time tests and surface roughness analysis were employed in the mechanism analysis of this investigation. The floatability of lignite was decreased with the pre-wetting increasing from 0 – 5min because the pores and fractures of lignite surface can be filled with water. However, the floatability of lignite was increased with the pre-wetting from 5 – 480min. NMR and SEM indicate that a long pre-wetting process (>5min) polished and rubbed the surface of lignite reducing the amount of macropores and fractures as well as the porosity. The rough lignite surface was also polished to be smooth. As the pre-wetting time increases, the topography of lignite surface, such as porosity, macropores, fractures and roughness decreased, which results in the decrease of water filling negative effects, and hence the floatability of lignite gradually increased with the pre-wetting time over 5min.

Bond-strength performance of hydraulic lime and natural cement mortared sandstone masonry

Flexural bond strength is an important performance characteristic of masonry structures yet there is no guidance for lime-mortared stonework in design codes of practice. This study investigates the bond strength of natural hydraulic lime (NHL) and natural cement mortared sandstone masonry. To this end, the flexural bond strength of masonry couplets, built with mortars of three hydraulic strengths and one natural cement and having a water-content adjusted to achieve a similar consistency, was measured with the bond wrench test. Practical mortar compositions and natural curing conditions were used within the experimental programme. Bond strength was found to be directly related to binder hydraulicity and sandstone pre-wetting time – a positive effect in the case of the former and a negative influence in the case of the latter. Pre-wetting time, however, had a greater influence on the feebly hydraulic lime binder (NHL 2) than on the moderately (NHL 3.5) and eminently hydraulic (NHL 5) lime binders. The results presented will assist in improving our knowledge of lime mortared sandstone masonry and in the development of design guidance.

The Effects of Conditioning Time on the Flotation of Oxidized Coal

In this investigation, the flotation behavior of oxidized coal affected by the conditioning time separated into two periods: prewetting time and collector conditioning time, were discussed. The prewetting time is 0 min, 1 min, 2 min, 3 min, 4 min, and 5 min, respectively. The collector conditioning time is 1 min, 2 min, 3 min, 4 min, 5 min, and 6 min, respectively. Fourier-transform infrared was used to analyze the chemical property of oxidized coal and fresh coal. The results show that the oxidized coal surface is more hydrophilic than the fresh coal. The results of flotation tests show that combustible matter recovery will be higher while the prewetting time is shorter. The mechanism of effects of conditioning time on the flotation of oxidized coal was discussed.

Effect of pre-wetting time on oxidized coal flotation

In this investigation, we discussed the flotation behavior of oxidized coal treated by different pre-wetting times. The pre-wetting time is 1min, 2min, 3min, 4min and 5min, respectively. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and contact angle measurements were used to indicate the surface properties of oxidized coal. XPS results show that the hydrophobicity of oxidized coal is very low and the oxidized coal should be pre-wetted quickly as there are many hydrophilic functional groups and few hydrophobic functional groups on the oxidized coal surface. In addition, there are also many cracks and holes on the oxidized coal surface from SEM pictures. The cracks and holes should be covered or filled up with water during pre-wetting process. Contact angle measurement results show that the contact angle between the water drop and oxidized coal surface decreases rapidly with the increase of measurement time. Both of the combustible matter recovery and concentrate ash content decrease with the increase of pre-wetting time.

Experiment Study on Mechanical Performance of Shale Lightweight Aggregate Concrete

High performance lightweight aggregate concrete is a kind of lightweight environment-protected building material with high strength, good workability, volume stability and durability, which is widely used in large scale engineering and some important engineering. In this paper water-binder ratio, fly ash content, pre-wetting time, sand ratio were tested to explore the comprehensive strength of lightweight aggregate concrete(LWAC). SEM was used to observe the microstructure characteristics of the specimens. The results showed that LWAC produced in the experiment present good performance, whose apparent density was 1760 Kg/m3～1930Kg/m3, 28d compressive strength was 55MPa～60MPa. Reasonable amounts of sand ratio(38%) and mineral admixtures(10%) were exited and the self-strength of lightweight aggregate played an important role in the preparation of LWAC. In the meanwhile, lightweight aggregates which were pre-wetted effectively increased the later strength.

Study on Water Permeability and Chloride Penetrability of the Shale Ceramsite Concrete

In this presented work, by the seepage experiment for three groups of shale ceramsite concrete with different mixing ratio, it produced its impermeability mark and analyzed how the three factors of pressure holding time, water cement ratio and ceramsite pre-wetting time to impact the penetration depth; also a three-layer neural network model was built up by collecting 20 groups of testing and experiment data of actual projects data of ceramsite concrete chloride penetrability, and performed the chloride experimental simulation and prediction with the model, got comparatively accurate predicted values of chloride permeability coefficient.The study results provide some reference for similar studies.

Experimental Study on Frost Resistance of the Shale Ceramsite Concrete

In this presented work, by freeze-thaw test for three groups of shale ceramsite concrete with different mix proportion, the experimental results show: the shale ceramsite concrete has preferable frost resistance property. After 100 times freeze-thaw cycles, its loss in weight and strength is very small; the frost resistance increases as ceramsite pre-wetting time is raised, and with the increasing of the water cement ratio, the frost resistance declines. The statement that ceramsite pre-wetting treatment is detrimental to frost resistance still deserves discussion, as it depends on the pore structure, water absorption characteristic and concrete air content of ceramsite itself. Meanwhile, freeze-thaw mechanism of the shale ceramsite concrete was analyzed in this paper. The study results provide some reference for other studies.

Analysis of prewetting conditions for old magazine papers before pulping in deinking

Recent research on deinking with an old newspaper (ONP)/old magazine (OMG) furnish and with a 100% ONP furnish demonstrates that the ink-substrate bond might not be sufficiently weakened within the short wetting time used in conventional pulping. If enough time for paper wetting is allowed before pulping, better ink detachment could be achieved when compared with conventional pulping. However, it has remained unclear how different prewetting conditions affect ink detachment and fragmentation when processing OMG-based furnish, such as supercalendered (SC) and lightweight coated (LWC) papers. In this study, we investigated the influence of prewetting time, temperature, and chemistry on the optical properties of rotogravure printed SC and heatset offset printed LWC-based pulps, when prewetting is performed without mechanical action before the actual pulping process. Different prewetting times (0-24 h) and temperatures (25°C-65°C) were tested with conventional alkaline soap chemistry and with reduced alkaline soap chemistry. The results for SC pulp support earlier findings and reveal that ink detachment can be improved by wetting SC paper with conventional deinking liquor before pulping. With SC paper, the longer the prewetting time, the lower the amount of attached ink after pulping. Ink that is printed on a coating (LWC paper) is easily detachable; therefore, its release cannot be improved by prewetting. Ink fragmentation was similar with and without prewetting treatment for SC- and LWC-based pulps.

Effect of lightweight aggregate pre-wetting on microstructure and permeability of mixed aggregate concrete

The influence of lightweight aggregate (LWA) pre-wetting on the chemical bound water and pore structure of the paste around aggregate as well as concrete permeability were investigated. The results show that, in early age the dry LWA has significant effect on the formation of dense paste around it and improving the concrete impermeability. However the prewetted LWA has strong water-releasing effect in later age, which increases the hydration degree of the paste around it, and makes the adjacent paste develop a structure with low porosity and finer aperture, furthermore the concrete impermeability can be improved. It is suggested that, as for concrete with low durability requirement, the LWA without pre-wetting treatment can be used as long as meet the workability requirement of fresh concrete, the good impermeability of concrete can be gained as well. As for concrete with high durability requirement, the prewetted LWA should be used, and the pre-wetting time should be extended as long as possible, in order to optimize the concrete structure in long term, and improve the concrete durability.

Influence of aggregate pre-wetting and fly ash on mechanical properties of lightweight concrete

This study has examined the mechanical properties of lightweight aggregate concrete with a density of 1800 kg/m 3. The effects of the following parameters on the concrete properties have been analyzed: the pre-wetting time of the lightweight aggregate and the percentage of pulverized fly ash used as cementitious replacement material. The strength of the lightweight aggregate was found to be the primary factor controlling the strength of high-strength lightweight concrete. An increase in the cementitious content from 420 to 450 kg/m 3 does not significantly increase the strength of lightweight aggregate concrete. The relationship between the flexural and compressive strength at 28 days can be represented by the equation f r =0.69√ f ck . The elastic modulus was found to be much lower than that of normal weight concrete, ranging from 15.0 to 20.3 GPa. The addition of PFA increases the slump and density of lightweight aggregate concrete.

Microstructure of pre-wetted aggregate on lightweight concrete

A study was made on microstructure and water absorption rate of ‘Litcon’—a porous lightweight aggregate made from expanded clay. EDAX analysis on the aggregate particle showed different chemical compositions between the shell and the inner core of the lightweight aggregate. S.E.M. examination on the resulting concrete showed a good mechanical bonding between the cement and the aggregate interface, though traces of inter-granular cracks were observed. When the pre-wetting time of the aggregate increased, the strength and the workability of the concrete increased too. The high workability of fresh concrete was attributed to the localised high water content at the surface of the pre-wetted aggregate. The surface pores of the aggregate shell absorbed the water built-up at the cement/aggregate transition phase thus resulting with lower water content at the transition zone. EDAX analysis confirmed migration of cement phase into the aggregate shell. This loss of fluidity at the transition zone may have a significant effect on the permeability of lightweight concrete.