Development Of Hydration Products Research Articles

Properties and mechanism of Cu(OH)2 nanoarray reinforced cement composites

This experiment investigates the effect of Cu(OH)2 nanoarray on the properties of cementitious materials. Cu(OH)2 nanoarray is a novel nanomaterial with excellent electrical conductivity and chemical stability. At present, the interaction mechanism between Cu(OH)2 nanoarray and cementitious materials has not been explored. In this paper, the effect of Cu(OH)2 nanoarray on the properties of cement mortar was investigated by testing the mechanical strength and electrical conductivity of Cu(OH)2 nanoarray. The microstructure of Cu(OH)2 nanoarray cement mortar and the development of hydration products were analyzed using XRD, SEM, EDS and MIP tests. The results showed that when 0.5% Cu(OH)2 nanoarray was added, the 28d compressive strength and flexural strength of the cement mortar increased by 50.29% and 41.28%, respectively, and its electrical resistivity decreased by 50%. The Cu(OH)2 nanoarray optimized the mechanical strength and workability of the cement mortar by modulating the hydration products and improving the microstructure.

The Effect of Magnetized Water on the Fresh and Hardened Properties of Slag/Fly Ash-Based Cementitious Composites

The physicochemical structure of the mixing water used in concrete has a significant effect on the physical and mechanical properties of cementitious composites. The studies on the effect of magnetized water (MW) on the properties of FA/BFS-based cementitious composites are still in their infancy. This study explores the effect of MW on the fresh and hardened properties of fly ash (FA)/blast furnace slag (BFS)-based cementitious composites. A total of 22 different mixture groups having FA/BFS (0, 5, 10, 15, 20, and 25%) by weight of cement were produced using tap water (TW) and MW. The fresh-state properties (the initial and final setting times and the consistency) and hardened-state properties (the compressive strength, water absorption properties, and rapid chloride ion permeability test) of produced cementitious composites were investigated. The development of hydration products was analyzed using scanning electron microscopy (SEM) and the mercury intrusion porosimetry (MIP) test. The results reveal that the fresh- and hardened-state properties of cementitious composite samples produced with MW are significantly improved. The properties of the samples utilizing MW showed that FA and BFS could be used at a higher rate for the same target properties in cementitious composites by using MW as mixing water. Using up to 25% FA/BFS in cementitious composites prepared with MW is recommended.

Mechanical and microstructural characterization of fly ash blended self-compacting concrete containing granite waste

This study examines the mechanical characteristics (compressive strength, split tensile and flexural strength) and microstructure characteristics (scanning electron microscopic (SEM), energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and Fourier transform infrared radiation (FTIR)) of fly ash blended self-compacting concrete (SCC) comprising of granite waste (GW). Mechanical performance of fly ash blended SCC augmented on the incorporation of up to 40% GW as a substitution of fine aggregate. SEM analysis revealed that the incorporation of GW densified the binder-aggregate matrix of resulting SCC. However, EDS, XRD and FTIR analysis revealed that there was a negligible effect of GW on the development of hydration products. It was thus concluded that the enhancement in the mechanical performance of the resulting SCC (prepared with GW) was mainly due to the filler efficacy of GW.

Hydration, Microstructure and Compressive Strength Development of Seawater-mixed Calcium Sulphoaluminate Cement-based Systems

In-depth understanding of the calcium sulphoaluminate (CSA) cement, a type of environment-friendly cement, is essential for its wide application in engineering practice. Partial replacement of CSA by alternative alumina-rich powders has significant potential in the production of cost-effective CSA cement. In this work various supplementary cementitious materials (SCMs) including slag, metakaolin and silica fume with different replacement levels were added into CSA cement, and mixing with seawater, to prepare paste and concrete specimens. The development of hydration products in the paste specimens was characterized by X-ray diffraction and Thermogravimetric analysis. The pore structures of the seawater-mixed paste specimens obtained from mercury intrusion porosimetry tests, along with the pH value and free chloride content in the pore solution, were analyzed. Results show that various SCMs have significantly different effects on the pore solution chemistry, hydration and microstructural formation of the seawater-mixed CSA cement, resulting in different mechanical behavior and durability properties. The results of this work are helpful for the development of cost-effective CSA cement-based concrete used in marine constructions.

Performance of rice husk Ash-Based sustainable geopolymer concrete with Ultra-Fine slag and Corn cob ash

This paper presents the first scientific attempt to develop and study the performance of rice husk ash (RHA) and ultra-fine slag (UFS) based sustainable geopolymer concrete with different ratio of corn cob ash (CCA). NaOH (8 M) and Na2SiO3 were employed as alkaline activators. CCA acted mainly as amorphous silica and was utilised as a substitute for RHA. The effects of different CCA contents (0%, 3%, 6%, 9% and 12% by RHA mass) on the performance of geopolymer concrete in terms of fresh, hardened and durability properties have been evaluated. Different characteristics, i.e. density, air content, workability, compressive, flexural and split tensile strengths, Young’s modulus of elasticity were investigated. Meanwhile, the durability performance was also evaluated by using different methods such as rapid chloride penetration test, chloride conductivity test, water sorptivity test and DIN (Deutsches Institut für Normung) water permeability test. The outcomes of this research have shown that UFS and CCA improved the compressive strength by 14–15%. They significantly improved the polymerisation and thus enhanced the strength and durability of sustainable geopolymer concrete. Furthermore, CCA and UFS acted as micro fillers and increased the CaO as well as SiO2 contents which enhanced the densification. Additionally, the development of hydration products in the matrix, enhanced the pore structure and thus the strength. This study revealed that CCA (up to 6%) can be utilised as a substitute binder to produce sustainable geopolymer concrete, and has the potential to replace conventional concrete for structural applications.

Autoclave-free ultra-early strength concrete preparation using an early strength agent and microstructure properties.

In this study, nano calcium silicate hydrate was used as an early strength agent to promote the compressive strength of concrete at 1 day. The strength development and the microstructure of standard concrete (SC), autoclave-free ultra-early strength concrete (ESC) and autoclaved concrete (AC) were comparatively studied. The development of hydration products, morphology and pore-structure with ages were investigated via XRD, TG, microhardness, SEM and NMR tests to reveal the mechanism of early strength of ESC. The results showed that the compressive strength of ESC at day 1 achieved 60% of the designed strength, as strong as 45.6 MPa, and only 3% less than that of SC after 90 days. While the compressive strength of AC was significant increased over 90% of ultimate at 1 day, then slightly raised after that. The hydration products did not changed between ESC and SC, but the content of C–S–H gel, Ca(OH)2 and non-evaporated water of ESC was higher in the same specific age. New hydration products such as hydrogarnet and tobermorite were found in AC under autoclave conditions. The microhardness of the paste and ITZ of ESC were also higher than those of SC. The porosity of ESC at 1 day was larger than that of SC, which was contributed by gel pores (1–10 nm). However, AC with higher ratio of large pores than ESC and SC exhibited the largest porosity. The results proved that nano calcium silicate hydrate as an early strength agent significantly increased the early strength of concrete under autoclave-free conditions. Nano calcium silicate hydrate particles supplied additional nucleus in pores and ITZ, accelerated the formation of C–S–H gel, hardened hydration products, and improved the porosity structure. However, with autoclave curing, the hydration products in AC formed with larger size and higher crystallization, which benefited for early strength. However, the large porosity with large size pores might cause damage.

Fracture behavior of lightweight foamed concrete: The crucial role of curing conditions

The mechanical behavior of lightweight foamed concrete (LWFC) is markedly affected by microstructural properties, related to the distribution of air bubbles and development of hydration products. In this paper an experimental study on notched beams made of LWFC is carried out, wherein Crack Mouth Opening Displacement (CMOD) is also monitored to compute the fracture energy. To investigate the influence of the curing conditions, half of the specimens are cured in air and the other half in water. Experimental evidence on the load-CMOD curve reveals that foamed concrete absorbs a significant amount of energy before rupture, and curing conditions play a crucial role on the resulting mechanical properties and fracture energy. Both flexural strength and fracture energy are significantly higher in air curing conditions, while such pronounced difference is not so apparent in terms of compressive strength, although better results are still achieved for air-cured specimens. This is further investigated through images of crack paths across the tested beams obtained by Field Emission Scanning Electron Microscopy (FESEM): for all the samples cured in air the presence of diffuse micro-cracks was noted, while those in water show less microcracks but different hydration products.

The Role of Alkalis in Hydraulic Mixtures

Alkali substances are present in cements used as a binder in concrete only in a minimum content. The most known process that alkali causes is the alkali-silica reaction. In this reaction, the alkali contained in the cement or supplied from the outside with an inappropriately selected aggregate containing amorphous SiO2. This reaction results in the development of hydration products, resulting in an increase in the volume of the original components, which can cause a breakage of the concrete structure and subsequent disintegration. The range of alkali-silica reaction can be reduced by the use of a suitable aggregate or the use of Type II admixtures which are characterized by pozzolanic or latently hydraulic activity. These admixtures react with alkali and then no longer react with the amorphous SiO2 contained in the aggregate. Alkalis also affect other properties of concrete such as basic physical-mechanical properties, frost resistance and pH.In the experimental part the pH values were compared between mixtures of Portland cement and alkaline activated blast furnace slag using slag aggregate from the heap Koněv.

Influence of Ultrafine 2CaO·SiO₂ Powder on Hydration Properties of Reactive Powder Concrete.

In this research, we assessed the influence of an ultrafine 2CaO·SiO2 powder on the hydration properties of a reactive powder concrete system. The ultrafine powder was manufactured through chemical combustion method. The morphology of ultrafine powder and the development of hydration products in the cement paste prepared with ultrafine powder were investigated by scanning electron microscopy (SEM), mineralogical composition were determined by X-ray diffraction, while the heat release characteristics up to the age of 3 days were investigated by calorimetry. Moreover, the properties of cementitious system in fresh and hardened state (setting time, drying shrinkage, and compressive strength) with 5% ordinary Portland cement replaced by ultrafine powder were evaluated. From SEM micrographs, the particle size of ultrafine powder was found to be up to several hundred nanometers. The hydration product started formulating at the age of 3 days due to slow reacting nature of belitic 2CaO·SiO2. The initial and final setting times were prolonged and no significant difference in drying shrinkage was observed when 5% ordinary Portland cement was replaced by ultrafine powder. Moreover, in comparison to control reactive powder concrete, the reactive powder concrete containing ultrafine powder showed improvement in compressive strength at and above 7 days of testing. Based on above, it can be concluded that the manufactured ultrafine 2CaO·SiO2 powder has the potential to improve the performance of a reactive powder cementitious system.

An Investigation on the Interfacial Transition Zone of Lightweight Aggregate Concrete

The technique of linking the SEM photographs taken around the interfacial transition zone area is applied to observe the development of hydration products for lightweight aggregate and paste at the different curing ages. This research first determines the mixture proportions of the two types of concrete specimens with different aggregate unit weights. The lightweight aggregate used is the sludge kilned aggregate from Shihmen reservoir. The very small SEM samples to be observed are taken from the concrete compressive test specimens and must include both aggregate and paste. The research then observes the hydration products (such as CH, C-S-H) of calcium ion and the pozzolanic reaction on the samples. Finally it assesses if the aggregate will produce ion exchange with cement and generate the hydration products. The hydration products on either side of the interface with a range of 100μm are observed using 2000x magnification. From the results, it is found that (1) the development of hydration products of the lightweight aggregate concrete is similar to that of the normal-weight aggregate concrete, (2) the failure at the 91 days age is that the lightweight aggregate is sheared, (3) the bond stress of aggregate and paste is controlled by hydration products of paste, (4) the aggregate has not interacted with cement paste to produce hydration products, and (5) the development of hydration products proves that the amount of binder used in the concrete specimen will affects its compressive strength.

Ultra Optimum Green Concrete Using High Volume Fly Ash Activated Systems

ABSTRACTEnvironmental issues related to CO2 emissions have become a key focus for many different industries, including the cement and concrete industry. An environmentally optimized ‘green’ concrete can provide a much needed alternative to conventional concrete to reduce the carbon foot-print of the construction industry. This can be achieved through high Portland cement replacement by fly ash and with the inclusion of activators to enhance the rate of development of strength and other properties. This study evaluates different fly ashes and different activators (Na2SO4, lime and quicklime) that are added to enhance the reaction of the fly ash to achieve a comparable performance to that of standard Portland cement in mixes of much lower CO2 emissions. TGA, XRD and SEM are used to determine the development of hydration products and the consumption of portlandite by the fly ash. It is found that the amorphous content of the fly ash is an important parameter influencing compressive strength evolution. Based on the results, Na2SO4 as an activator, and a fly ash with high reactive SiO2 and Al2O3 contents and low Fe2O3 are found to provide the best options for producing a high volume fly ash matrix with the potential to show comparable behavior to a Portland cement control mix.

The Effect of Fly Ash on the Hydration of Cements At Low Temperature Mixed and Cured in Sea-Water

ABSTRACTThe use of fly ash as a partial replacement in cements is widespread because of reduced costs and the reported improvement in performance. Fly ash/cement blends have been used offshore for underbase grouting of gravity platforms, although the cold marine exposure may slow the pozzolanic reaction which is very sensitive to temperature. Sea-water could be used as mixing water under these conditions. This paper looks at how curing at 8°C, the use of sea-water as mixing water, and direct exposure to sea-water, influence the hydration, strength and microstructural development of an OPC and an SRPC with 30% fly ash replacement. The early heat evolution was measured with a conduction calorimeter, while the presence and development of hydration products were identified by DTA, TG and x-ray analysis. Scanning electron microscopy was used in two modes; secondary electron images of fracture surfaces were examined, and a quantitative description of microstructure was made possible by analysis of backscattered electron images of polished sections. The morphology and distribution of hydration products in the wet state was studied using an environmental cell in a high voltage electron microscope.