scholarly journals Does a High Amount of Unhydrated Portland Cement Ensure an Effective Autogenous Self-Healing of Mortar?

Materials ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3298 ◽  
Author(s):  
Magdalena Rajczakowska ◽  
Lennart Nilsson ◽  
Karin Habermehl-Cwirzen ◽  
Hans Hedlund ◽  
Andrzej Cwirzen
Keyword(s):  
Portland Cement ◽  
High Performance ◽  
Cement Content ◽  
Healing Process ◽  
Self Healing ◽  
Aging Effects ◽  
Cement Ratio ◽  
Dense Microstructure ◽  
Water To Cement Ratio ◽  
Very High

It is commonly accepted that the autogenous self-healing of concrete is mainly controlled by the hydration of Portland cement and its extent depends on the availability of anhydrous particles. High-performance (HPCs) and ultra-high performance concretes (UHPCs) incorporating very high amounts of cement and having a low water-to-cement ratio reach the hydration degree of only 70–50%. Consequently, the presence of a large amount of unhydrated cement should result in excellent autogenous self-healing. The main aim of this study was to examine whether this commonly accepted hypothesis was correct. The study included tests performed on UHPC and mortars with a low water-to-cement ratio and high cement content. Additionally, aging effects were verified on 12-month-old UHPC samples. Analysis was conducted on the crack surfaces and inside of the cracks. The results strongly indicated that the formation of a dense microstructure and rapidly hydrating, freshly exposed anhydrous cement particles could significantly limit or even hinder the self-healing process. The availability of anhydrous cement appeared not to guarantee development of a highly effective healing process.

scholarly journals Effect of Flyash Addition on Mechanical and Gamma Radiation Shielding Properties of Concrete

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Kanwaldeep Singh ◽  
Sukhpal Singh ◽  
Gurmel Singh
Keyword(s):  
Gamma Radiation ◽  
Attenuation Coefficient ◽  
Cement Content ◽  
Mass Attenuation Coefficient ◽  
Radiation Shielding ◽  
Mechanical Parameters ◽  
Cement Ratio ◽  
Concrete Mixtures ◽  
Water To Cement Ratio ◽  
Shielding Properties

Six concrete mixtures were prepared with 0%, 20%, 30%, 40%, 50%, and 60% of flyash replacing the cement content and having constant water to cement ratio. The testing specimens were casted and their mechanical parameters were tested experimentally in accordance with the Indian standards. Results of mechanical parameters show their improvement with age of the specimens and results of radiation parameters show no significant effect of flyash substitution on mass attenuation coefficient.

scholarly journals Microencapsulated healing agents for an elevated-temperature cured epoxy: Influence of viscosity on healing efficiency

2021 ◽  
pp. 096739112110453
Author(s):  
Habibah Ghazali ◽  
Lin Ye ◽  
Amie N Amir
Keyword(s):  
Fracture Toughness ◽  
Elevated Temperature ◽  
High Performance ◽  
Healing Process ◽  
Polymer Network ◽  
Diglycidyl Ether ◽  
The Self ◽  
Effect Of Temperature ◽  
Mode I ◽  
Self Healing

Among many applications, elevated-temperature cured epoxy resins are widely used for high-performance applications especially for structural adhesive and as a matrix for structural composites. This is due to their superior chemical and mechanical properties. The thermosetting nature of epoxy produces a highly cross-linked polymer network during the curing process where the resulting material exhibited excellent properties. However, due to this cross-linked molecular structure, epoxies are also known to be brittle, and once a crack initiated in the material, it is difficult to arrest the crack propagation. Earlier research found that the inclusion of encapsulated healing agents is able to introduce self-healing ability to the room-temperature cured epoxies. The current study investigated the self-healing behaviour of an elevated-temperature cured epoxy, which incorporated the dual-capsule system loaded with diglycidyl-ether of bisphenol-A (DGEBA) resin and mercaptan. The microcapsules were prepared by the in-situ polymerisation method while the fracture toughness and the self-healing capability of the tapered-double-cantilever-beam (TDCB) epoxy specimens were measured under Mode-I fracture toughness testing. We investigated the effect of temperature on viscosity of the healing agents and how these values influence the formation of uniform healing on the fracture surfaces. It was found that incorporation of the dual-capsule self-healing system onto an elevated-temperature cured epoxy slightly changed the fracture toughness of the epoxy as indicated by the Mode-I testing. In the case of thermal healing at 70°C, the self-healing epoxy exhibited a recovery of up to 111% of its original fracture toughness, where a uniform spreading of the healant was observed. The excellent healing behaviour is attributed to the lower viscosity of the healant at higher temperature and the higher glass transition temperature ( Tg) of the produced healant film. The DSC analysis confirmed that the healing process was not contributed by the post-curing of the host epoxy.

scholarly journals Influence of Cement Type and Water-to-Cement Ratio on the Formation of Thaumasite

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Ailian Zhang ◽  
Linchun Zhang
Keyword(s):  
Portland Cement ◽  
Cement Mortar ◽  
Sulfate Solution ◽  
Sulfate Attack ◽  
Strength Development ◽  
X Ray Diffraction ◽  
Limestone Filler ◽  
Visual Appearance ◽  
Cement Ratio ◽  
Water To Cement Ratio

Cement mortar prisms were prepared with three different cement types and different water-to-cement ratios plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at 5°C and the visual appearance and strength development for every mortar were measured at intervals up to 1 year. Samples selected from the surface of prisms after 1-year immersion were examined by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results show that mortars with sulfate resisting Portland cement (SRC) or sulphoaluminate cement (SAC) underwent weaker degradation due to the thaumasite form of sulfate attack than mortars with ordinary Portland cement (OPC). A lower water-to-cement ratio leads to better resistance to the thaumasite form of sulfate attack of the cement mortar. A great deal of thaumasite or thaumasite-containing materials formed in the OPC mortar, and a trace of thaumasite can also be detected in SRC and SAC mortars. Therefore, the thaumasite form of sulfate attack can be alleviated but cannot be avoided by the use of SAC or SRC.

scholarly journals Control of Drying Shrinkage of Magnesium Silicate Hydrate Gel Cements

2016 ◽  
Vol 709 ◽  
pp. 109-113 ◽  
Author(s):  
Ting Ting Zhang ◽  
Xiao Min Liang ◽  
M. Lorin ◽  
Zhen Lin Wu ◽  
Chris Cheeseman ◽  
...  
Keyword(s):  
Portland Cement ◽  
Magnesium Oxide ◽  
Silica Fume ◽  
Drying Shrinkage ◽  
Magnesium Silicate ◽  
Hydration Products ◽  
Cement Ratio ◽  
Water To Cement Ratio ◽  
Order Of Magnitude ◽  
Forced Drying

Cracks were observed when the magnesium silicate hydrate gel cement (prepared by 40% MgO/ 60% silica fume) was dried. This drying cracking is believed to be caused when unbound water evaporates from the binder. The shrinkage upon forced drying to 200 °C of mortars made up from a reactive magnesium oxide, silica fume and sand was measured using dilatometry. The magnitude of the drying shrinkage was found to decrease when more sand or less water was added to the mortars and can be as low as 0.16% for a mortar containing 60 wt% sand and a water to cement ratio of 0.5, which is of a similar order of magnitude as observed in Portland cement based mortars and concretes. A simple geometrical interpretation based on packing of the particles in the mortar can explain the observed drying shrinkages and based on this analysis the drying shrinkage of the hydration products at zero added solid is estimated to be 7.3% after 7 days of curing.

scholarly journals Polymer nanocomposite-enabled high-performance triboelectric nanogenerator with self-healing capability

RSC Advances ◽  
2018 ◽  
Vol 8 (54) ◽  
pp. 30661-30668 ◽  
Author(s):  
Huidan Niu ◽  
Xinyu Du ◽  
Shuyu Zhao ◽  
Zuqing Yuan ◽  
Xiuling Zhang ◽  
...  
Keyword(s):  
High Performance ◽  
Healing Process ◽  
Polymer Nanocomposite ◽  
The Self ◽  
Triboelectric Nanogenerator ◽  
Self Healing

The self-healing process and the primary characteristics showing the performance of the self-healed triboelectric nanogenerator.

Experimental Study on Engineering Performance of Portland Cement Stabilization of Soil-Bentonite

2011 ◽  
Vol 179-180 ◽  
pp. 978-982
Author(s):  
Xiao Yong Li ◽  
Zhi Gang Zhang
Keyword(s):  
Hydraulic Conductivity ◽  
Portland Cement ◽  
Cement Content ◽  
Expansion Ratio ◽  
Wall Material ◽  
Experimental Program ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Cement Ratio ◽  
Water Cement Ratio

Slurry trench cutoff walls, constructed using self-hardening cement-bentonite (SCB) are the most common form of in-ground vertical contaminant barrier in the world, and are increasingly being used in China. As a kind of vertical anti-seepage wall material， SCB slurry is requently used for the containment of contaminated groundwater and other envirofunental Protection Projeets abroad. Domestie applieation of cement-bentonite slurry walls is not extensive. The objective of this study was to evaluate the effect of water-cement ratio and cement content on the hydraulic behavior of SCB and soil–bentonite (SB) mixtures permeated with water. The experimental program included unconfined compression tests, expansion ratio tests and hydraulic conductivity tests. The test results indicated changes in hydraulic conductivity take place due to the variation of the water-cement ratio and permeant fluid. Cement is a main material in effecting the CSB strength of unconfined compression. Cement greatly influenced the CSB permeability coefficient. Addition of Portland cement to the SB mixtures increased their hydraulic conductivity when permeated with water. The hydraulic conductivity of the SCB specimens permeated with water was inversely related to the cement content.

Sign in / Sign up

Export Citation Format

Share Document