New developments in understanding the chemistry of cement hydration

1983 ◽  
Vol 310 (1511) ◽  
pp. 53-66 ◽  
Keyword(s):  
Cement Hydration ◽  
Hydration Product ◽  
Solution Chemistry ◽  
Strength Development ◽  
Microstructural Development ◽  
Cement Pastes ◽  
Complex Process ◽  
Calcium Aluminates ◽  
Colloidal Gel ◽  
Reaction With Water

Portland cement is based on calcium silicates with lesser amounts.of calcium aluminates. Its reaction with water, which is responsible for strength development, is a complex process involving the precipitation of hydration products in colloidal gel and crystalline forms. This paper describes the microstructural development of the hydrates the structure of colloidal C—S—H gel, which is the main hydration product, the kinetics of hydration and the aqueous solution chemistry of cement pastes and pastes made with pure C 3 S. Theories relating to the mechanism of cement hydration are examined and these are discussed in terms of studies of the effect of accelerating and retarding admixtures for cement.

scholarly journals Influence of Carbon Nanotubes on the Mechanical Behavior and Porosity of Cement Pastes Prepared by A Dispersion on Cement Particles in Isopropanol Suspension

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3164 ◽  
Author(s):  
Vanessa Vilela Rocha ◽  
Péter Ludvig
Keyword(s):  
Carbon Nanotubes ◽  
Cement Hydration ◽  
Hydration Product ◽  
Image Correlation ◽  
Superior Performance ◽  
Cement Pastes ◽  
Three Point Bending ◽  
Flexural Tensile Strength ◽  
Nucleation Sites ◽  
Effective Dispersion

Cement composites prepared with nanoparticles have been widely studied in order to achieve superior performance structures. The incorporation of carbon nanotubes (CNTs) is an excellent alternative due to their mechanical, electrical, and thermal properties. However, effective dispersion is essential to ensure strength gains. In the present work, cement pastes were prepared incorporating CNTs in proportions up to 0.10% by weight of cement, dispersed on the surface of anhydrous cement particles in isopropanol suspension and using ultrasonic agitation. Digital image correlation was employed to obtain basic mechanical parameters of three-point bending tests. The results indicated a 34% gain in compressive strength and 12% in flexural tensile strength gains, respectively, as well as a 70% gain in fracture energy and 14% in fracture toughness in the presence of 0.05% CNTs were recorded. These results suggest that CNTs act as crack propagation controllers. Moreover, CNT presence contributes to pore volume reduction, increases the density of cement pastes, and suggests that CNTs additionally act as nucleation sites of the cement hydration products. Scanning electron microscopy images indicate effective dispersion as a result of the methodology adopted, plus strong bonding between CNTs and the cement hydration product. Therefore, CNTs can be used to obtain more resistant and durable cement-based composites.

scholarly journals On the Feasibility of Using Industrial Urea to Mitigate Thermal and Shrinkage Cracking in Concrete

2021 ◽  
Vol 11 (6) ◽  
pp. 2483
Author(s):  
Hak-Young Kim
Keyword(s):  
Shrinkage Strain ◽  
Hydration Product ◽  
Heat Of Hydration ◽  
Nitrogen Fertilizers ◽  
Strength Development ◽  
Mixing Ratio ◽  
Mixing Ratios ◽  
Physiological Processes ◽  
Compressive Strength Development ◽  
Reaction With Water

Industrial urea is an organic compound that is widely used for various physiological processes and for producing nitrogen fertilizers. This study hypothesized that mixing urea with concrete would decrease the temperature and expansion of the cement microstructure abruptly due to the reaction with water and a cement hydration product. This study tested the hypothesis by experiments. The performance of concrete was evaluated after setting the mixing ratio of industrial urea was to 0%, 5%, 10%, and 15%. The results showed that temperature decreased drastically immediately after mixing and the decrease in temperature increased with a higher mixing ratio. Consequently, condensation was delayed, and heat of hydration decreased. It was found that when considering workability and compressive strength development performance, the proper mixing ratio of urea was around 10%. This study proposed the mixing design technique of concrete mixed with urea. Additionally, this study reported better carbonation resistance and mitigated shrinkage strain of concrete mixed with urea compared to existing low-heat mixing ratios.

scholarly journals The effects of seawater on the hydration, microstructure and strength development of Portland cement pastes incorporating colloidal silica

2019 ◽  
Vol 10 (8) ◽  
pp. 2627-2638 ◽  
Author(s):  
Pawel Sikora ◽  
Krzysztof Cendrowski ◽  
Mohamed Abd Elrahman ◽  
Sang-Yeop Chung ◽  
Ewa Mijowska ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Synergistic Effect ◽  
Portland Cement ◽  
Colloidal Silica ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Hydration Kinetics ◽  
Cement Pastes ◽  
Noticeable Improvement

AbstractThis contribution investigates the effects of seawater and colloidal silica (NS) in the amounts of 1, 3 and 5 wt%, respectively, on the hydration, strength development and microstructural properties of Portland cement pastes. The data reveal that seawater has an accelerating effect on cement hydration and thus a significant contribution to early strength development was observed. The beneficial effect of seawater was reflected in an improvement in compressive strength for up to 14 days of hydration, while in the 28 days compressive strength values were comparable to that of cement pastes produced with demineralized water. The combination of seawater and NS significantly promotes cement hydration kinetics due to a synergistic effect, resulting in higher calcium hydroxide (CH) production. NS can thus react with the available CH through the pozzolanic reaction and produce more calcium silicate hydrate (C-S-H) gel. A noticeable improvement of strength development, as the result of the synergistic effect of NS and seawater, was therefore observed. In addition, mercury intrusion porosimetry (MIP) tests confirmed significant improvements in microstructure when NS and seawater were combined, resulting in the production of a more compact and dense hardened paste structure. The optimal amount of NS to be mixed with seawater, was found to be 3 wt% of cement.

scholarly journals Electrochemical cell design and impedance spectroscopy of cement hydration

2020 ◽  
Vol 56 (2) ◽  
pp. 1203-1220
Author(s):  
Aldo F. Sosa Gallardo ◽  
John L. Provis
Keyword(s):  
Impedance Spectroscopy ◽  
Cement Hydration ◽  
Electrochemical Cell ◽  
Solid Phase ◽  
Data Interpretation ◽  
Microstructural Development ◽  
Cell Design ◽  
Cement Pastes ◽  
Impedance Measurements ◽  
Parasitic Effects

Abstract Understanding the complexity of the chemical and microstructural evolution of cement during hydration remains a controversial subject, and although numerous techniques have been used to assess this process, further insight is still needed. Alternating current impedance spectroscopy has been demonstrated to be a sensitive and powerful technique for cement characterisation in both fresh and hardened states; however, it has also shown certain experimental limitations (e.g. data interpretation, electrode, and parasitic effects) that prevent its wider acceptance. This study assesses electrochemical cell design and the impedance response during cement hydration. The results show that a significant decrease in the parasitic effects at high frequencies (caused mainly by leads and electrode effects) can be achieved through an optimal cell design and impedance measurements correction, enabling correlation of impedance measurements to particular aspects of the cement hydration process. However, due the limited solid phase microstructural development and the high conductivity of cement paste at low degrees of hydration, the parasitic effects could not be fully eliminated for fresh or early-age cement pastes.

Understanding cement hydration at the microscale: new opportunities from `pencil-beam' synchrotron X-ray diffraction tomography

2013 ◽  
Vol 46 (1) ◽  
pp. 142-152 ◽  
Author(s):  
Marco Voltolini ◽  
Maria Chiara Dalconi ◽  
Gilberto Artioli ◽  
Matteo Parisatto ◽  
Luca Valentini ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Cement Hydration ◽  
Tomographic Reconstruction ◽  
Microstructural Development ◽  
Diffraction Tomography ◽  
Pencil Beam ◽  
X Ray Diffraction ◽  
Cement Pastes ◽  
X Ray ◽  
Filtering Procedure

The present work describes some new improvements concerning the analysis of cement hydration processes using `pencil-beam' synchrotron X-ray diffraction tomography. (i) A new filtering procedure, applied to the diffraction images, has been developed to separate the powder-like contribution from that of the grains in the diffraction images. (ii) In addition to improving the quality of the diffraction images for the subsequent analysis and tomographic reconstruction, the filtering procedure can also be used to perform a qualitative analysis of the crystallite size distribution, whenever the more standard approaches cannot be applied. (iii) Given the importance of the calcium silicate hydrate phase (C–S–H) in cements, a procedure to obtain its spatial distribution using the diffraction signal has been successfully applied, even though C–S–H is a highly disordered phase, almost amorphous to X-ray diffraction. (iv) The main result of this study has been to show that, in spite of the long measurement times required, it is possible to usein situexperiments at different aging times of cement pastes to monitor the cement evolution. This allowed the evolution of the microstructure during the acceleration and deceleration periods of the hydration process to be checked with unprecedented detail, since the quantitative spatial distribution of each phase (including C–S–H) dissolved or precipitated in the sample has been obtained. The reported approach opens up a range of opportunities for the investigation of complex multiphase systems and processes, including hydration and microstructural development in cements.

scholarly journals The Influence of Water Reducing Agents on Early Hydration Property of Ferrite Aluminate Cement Paste

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 731
Author(s):  
Chunlong Huang ◽  
Zirui Cheng ◽  
Jihui Zhao ◽  
Yiren Wang ◽  
Jie Pang
Keyword(s):  
Setting Time ◽  
Critical Role ◽  
Hydration Product ◽  
Reducing Agents ◽  
Reducing Agent ◽  
Hydration Process ◽  
Early Hydration ◽  
Cement Pastes ◽  
Hydration Rate ◽  
Aluminate Cement

The ferrite aluminate cement (FAC) could rapidly lose fluidity or workability due to its excessive hydration rate, and greatly reduce the construction performance. Chemical admixtures are commonly used to provide the workability of cement-based materials. In this study, to ensure required fluidity of FAC, chemically different water reducing agents are incorporated into the FAC pastes. The experiments are performed with aliphatic water reducing agent (AP), polycarboxylic acid water reducing agent (PC) and melamine water reducing agent (MA), respectively. Influence of the water reducing agents on fluidity, setting time, hydration process, hydration product and zeta potential of the fresh cement pastes is investigated. The results show that PC has a better dispersion capacity compared to AP and MA. Besides decreasing water dosage, PC also acts as a retarder, significantly increasing the setting times, delaying the hydration rate and leading to less ettringite in the hydration process of FAC particles. The water reducing agents molecules are adsorbed on the surface of positively charged minerals and hydration products, however, for PC, steric hindrance from the long side chain of PC plays a critical role in dispersing cement particles, whereas AP and MA acting through an electrostatic repulsion force.

Assessment of Hydration Degree of Cement in the Fly Ash-Cement Pastes Based on the Calcium Hydroxide Content

2014 ◽  
Vol 875-877 ◽  
pp. 177-182 ◽  
Author(s):  
Xiang Li ◽  
Hua Quan Yang ◽  
Ming Xia Li
Keyword(s):  
Fly Ash ◽  
Calcium Hydroxide ◽  
Cement Hydration ◽  
Ash Content ◽  
Content Increase ◽  
Hydration Degree ◽  
Equilibrium Calculation ◽  
Cement Pastes ◽  
Cement Ratio ◽  
Water Cement Ratio

The hydration degree of fly ash and the calcium hydroxide (CH) content were measured. Combined with the equilibrium calculation of cement hydration, a new method for assessment of the hydration degree of cement in the fly ash-cement (FC) pastes based on the CH content was developed. The results reveal that as the fly ash content increase, the hydration degree of fly ash and the CH content decrease gradually; at the same time, the hydration degree of cement increase. The hydration degree of cement in the FC pastes containing a high content of fly ash (more than 35%) at 360 days is as high as 80%, even some of which hydrates nearly completely. The effect of water-cement ratio to the hydration degree of cement in the FC pastes is far less distinct than that of the content of fly ash.

scholarly journals Reutilizing Waste Iron Tailing Powders as Filler in Mortar to Realize Cement Reduction and Strength Enhancement

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 541
Author(s):  
Liyun Cui ◽  
Peiyuan Chen ◽  
Liang Wang ◽  
Ying Xu ◽  
Hao Wang
Keyword(s):  
Cement Hydration ◽  
Mercury Intrusion Porosimetry ◽  
Economic Cost ◽  
Strength Development ◽  
Effective Utilization ◽  
Strength Enhancement ◽  
Nucleation Effect ◽  
Practical Engineering ◽  
Internal Mechanism ◽  
Massive Accumulation

Recently, the massive accumulation of waste iron tailings powder (WITP) has resulted in significant environmental pollution. To solve this problem, this paper proposes an original mortar replacement (M) method to reuse waste solids and reduce cement consumption. In the experiment, the author employed an M method which replaces water, cement, and sand with WITP under constant water/cement and found that the strength development can be significantly improved. Specifically, a mortar with 20% WITP replacement can obtain a 30.95% improvement in strength development. To study the internal mechanism, we performed experiments such as thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), and SEM. The results demonstrate that the nucleation effect and pozzolanic effect of WITP can help promote cement hydration, and MIP reveals that WITP can effectively optimize pore structure. In addition, 1 kg 20% WITP mortar reduced cement consumption by 20%, which saves 19.98% of the economic cost. Comprehensively, our approach achieves the effective utilization of WITP and provides a favorable reference for practical engineering.

scholarly journals Effect of nano-SnO2 on early-age hydration of Portland cement paste

2019 ◽  
Vol 11 (6) ◽  
pp. 168781401985194 ◽  
Author(s):  
Jianping Zhu ◽  
Genshen Li ◽  
Ruijie Xia ◽  
Huanhuan Hou ◽  
Haibin Yin ◽  
...  
Keyword(s):  
Portland Cement ◽  
Cement Paste ◽  
Cement Hydration ◽  
Cementitious Materials ◽  
Hydration Process ◽  
Strength Development ◽  
Early Age ◽  
Test Machine ◽  
Portland Cement Paste ◽  
Scanning Electron

Nanomaterial, as a new emerging material in the field of civil engineering, has been widely utilized to enhance the mechanical properties of cementitious material. Nano-SnO2 has presented high hardness characteristics, but there is little study of the application of nano-SnO2 in the cementitious materials. This study mainly investigated the hydration characteristics and strength development of Portland cement paste incorporating nano-SnO2 powders with 0%, 0.08%, and 0.20% dosage. It was found that the early-age compressive strength of cement paste could be greatly improved when nano-SnO2 was incorporated with 0.08% dosage. The hydration process and microstructure were then measured by hydraulic test machine, calorimeter, nanoindentation, X-ray diffraction, scanning electron microscope, and mercury intrusion porosimetry. It was found that the cement hydration process was promoted by the addition of nano-SnO2, and the total amount of heat released from cement hydration is also increased. In addition, the addition of nano-SnO2 can promote the generations of high density C-S-H and reduce the generations of low density C-S-H indicating the nucleation effect of nano-SnO2 in the crystal growth process. The porosity and probable pore diameter of cement paste with 0.08% nano-SnO2 were decreased, and the scanning electron microscopic results also show that the cement paste with 0.08% nano-SnO2 promotes the densification of cement microstructure, which are consistent with the strength performance.

Sign in / Sign up

Export Citation Format

Share Document