scholarly journals Experimental Investigation and Theoretical Modeling of Nanosilica Activity in Concrete

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Han-Seung Lee ◽  
Hyeong-Kyu Cho ◽  
Xiao-Yong Wang
Keyword(s):  
Compressive Strength ◽  
Calcium Hydroxide ◽  
Blended Cement ◽  
Bound Water ◽  
Pozzolanic Reaction ◽  
Theoretical Modeling ◽  
Experimental Investigations ◽  
Hydration Reaction ◽  
Degree Of Hydration ◽  
Water Contents

This paper presents experimental investigations and theoretical modeling of the hydration reaction of nanosilica blended concrete with different water-to-binder ratios and different nanosilica replacement ratios. The developments of chemically bound water contents, calcium hydroxide contents, and compressive strength of Portland cement control specimens and nanosilica blended specimens were measured at different ages: 1 day, 3 days, 7 days, 14 days, and 28 days. Due to the pozzolanic reaction of nanosilica, the contents of calcium hydroxide in nanosilica blended pastes are considerably lower than those in the control specimens. Compared with the control specimens, the extent of compressive strength enhancement in the nanosilica blended specimens is much higher at early ages. Additionally, a blended cement hydration model that considers both the hydration reaction of cement and the pozzolanic reaction of nanosilica is proposed. The properties of nanosilica blended concrete during hardening were evaluated using the degree of hydration of cement and the reaction degree of nanosilica. The calculated chemically bound water contents, calcium hydroxide contents, and compressive strength were generally consistent with the experimental results.

scholarly journals Prediction of Chloride Penetration into Hardening Concrete

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Wei-Jie Fan ◽  
Xiao-Yong Wang
Keyword(s):  
Cement Hydration ◽  
Binding Capacity ◽  
Numerical Procedure ◽  
Chloride Ion ◽  
Chloride Ions ◽  
Experimental Investigations ◽  
Hydration Reaction ◽  
Degree Of Hydration ◽  
Chloride Diffusivity ◽  
Chloride Ion Penetration

In marine and coastal environments, penetration of chloride ions is one of the main mechanisms causing concrete reinforcement corrosion. Currently, most of experimental investigations about submerged penetration of chloride ions are started after the four-week standard curing of concrete. The further hydration of cement and reduction of chloride diffusivity during submerged penetration period are ignored. To overcome this weak point, this paper presents a numerical procedure to analyze simultaneously cement hydration reaction and chloride ion penetration process. First, using a cement hydration model, degree of hydration and phase volume fractions of hardening concrete are determined. Second, the dependences of chloride diffusivity and chloride binding capacity on age of concrete are clarified. Third, chloride profiles in hardening concrete are calculated. The proposed numerical procedure is verified by using chloride submerged penetration test results of concrete with different mixing proportions.

scholarly journals Hydration and Microstructure of Cement Pastes with Calcined Hwangtoh Clay

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 458 ◽  
Author(s):  
Run-Sheng Lin ◽  
Xiao-Yong Wang ◽  
Han-Seung Lee ◽  
Hyeong-Kyu Cho
Keyword(s):  
Compressive Strength ◽  
Inductively Coupled Plasma ◽  
Early Stage ◽  
Isothermal Calorimetry ◽  
Blended Cement ◽  
Bound Water ◽  
Dilution Effect ◽  
Attenuated Total Reflection ◽  
Chemical Effect ◽  
X Ray

Calcined Hwangtoh (HT) clay is a very promising supplementary cementitious material (SCM). In this work, the development of the mechanical properties and microstructures of HT-blended cement paste was studied after substituting the binder with HT powder calcined at 800 °C. The water-to-binder (w/b) ratios of the paste used were 0.2 and 0.5, and the quantities of HT powder added to the mixture were 0, 10, and 20%. The compressive strength test indicates that the addition of the HT powder increases the compressive strength of the paste after seven days of curing, and the highest compressive strength is obtained with the 10% HT substitution, regardless of whether the w/b ratio is 0.5 or 0.2. X-ray fluorescence (XRF), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), isothermal calorimetry, thermogravimetric analysis (TGA), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analysis show that the HT powder not only has a physical effect (i.e., nucleation effect and dilution effect) on cement hydration but also has a chemical effect (i.e., chemical reaction of HT). The results of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analysis show that the paste has more ettringite during the early stage, and the microstructure is refined after the addition of the HT powder. In addition, the relationships between chemically bound water, hydration heat, and compressive strength are presented.

scholarly journals Strength development of cement-treated sand using different cement types cured at different temperatures

2018 ◽  
Vol 195 ◽  
pp. 01006
Author(s):  
Lanh Si Ho ◽  
Kenichiro Nakarai ◽  
Kenta Eguchi ◽  
Takashi Sasaki ◽  
Minoru Morioka
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Cement Content ◽  
Bound Water ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Different Temperatures ◽  
Early Strength

This study aimed to investigate the strength development of cement-treated sand using different cement types: ordinary Portland cement (OPC), high early strength Portland cement (HPC), and moderate heat Portland cement (MPC) cured at different temperatures. The cementtreated sand specimens were prepared with 8% of cement content and cured under sealed conditions at 20οC and 40οC, and mortar specimens were also prepared for reference. The results showed that the compressive strength of cement-treated sand increased in order of MPC, OPC, and HPC under high curing temperatures. It was interesting that the compressive strength of the specimens using HPC was much larger than that of the specimen using OPC and MPC under 20οC due to the larger amount of chemically bound water. Additionally, it was revealed that under high curing temperatures, the pozzolanic reaction was accelerated in the cement-treated sand; this may be caused by the high proportions of sand in the mixtures.

scholarly journals USE OF FINE GROUND DUNE SAND AS A SUPPLEMENTARY CEMENTING MATERIAL

2014 ◽  
Vol 20 (1) ◽  
pp. 32-37 ◽  
Author(s):  
Abdulrahman Alhozaimy ◽  
Omer Abdalla Alawad ◽  
Mohd Saleh Jaafar ◽  
Abdulaziz Al-Negheimish ◽  
Jamaloddin Noorzaei
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Calcium Hydroxide ◽  
Pozzolanic Reaction ◽  
Dune Sand ◽  
Cement Production ◽  
Curing Conditions ◽  
High Consumption ◽  
Autoclave Curing ◽  
Cementing Material

The process of Portland cement production is associated with high consumption of energy and resources. Therefore, there is a need to replace the Portland cement with environmental friendly materials. This study was conducted to determine the feasibility of using ground dune sand as cement replacement materials under different curing conditions. Portland cement was replaced by ground dune sand at five levels of replacement (0–40% by weight). The compressive strength of mortar under standard and autoclave curing conditions and the influence of different autoclave temperatures and durations were investigated. The microstructure of selected mixtures was analyzed by XRD and SEM. Results showed that the compressive strength under the standard curing decreased as the level of replacement increased. However, under autoclave curing compressive strength increased as the content of ground dune sand increased. XRD and SEM revealed the absence of calcium hydroxide and the formation of secondary calcium silicate hydrate. The improvement of compressive strength and the absence of calcium hydroxide under autoclave curing indicated that the pozzolanic reaction between silica of dune sand and calcium hydroxide occurred.

scholarly journals Experimental Study on Mechanical Properties of Fly Ash Stabilized with Cement

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Shengquan Zhou ◽  
Yongfei Zhang ◽  
Dawei Zhou ◽  
Weijian Wang ◽  
Dongwei Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Fly Ash ◽  
Early Stage ◽  
Strain Curve ◽  
Pozzolanic Reaction ◽  
Hydration Reaction ◽  
Hydration Products ◽  
Compressive Test ◽  
Plastic Properties

Cement-fly ash mixture has been commonly used for the foundation treatment projects in the fly ash stratum, as it is effective in improving foundation bearing capacity and reducing settlement of stratum. In order to figure out the effect of dynamic and static load on the mechanical properties exhibited by the cement-fly ash and the reaction mechanism of cement-fly ash, a combination of the unconfined compressive test, impact test, scanning electron microscopy (SEM), and X-ray diffraction (XRD) method was adopted in this study to investigate the cement-fly ash test samples. As demonstrated by the results, the observed growth rate of 0–60 days (d) is higher than that in the later stages and the typical stress-strain curve can be divided into six sections under the unconfined compressive test. At the gas pressure of 0.2 MPa, the cement-fly ash samples exhibited obvious plastic properties in early curing time (0–60 d), and brittle failure was observed in the final stage (90 d). It is obvious that the value of dynamic compressive strength (DCS) is higher than that of unconfined compressive strength (UCS). The analysis of XRD has revealed that the hydration products are primarily derived from the hydration reaction of cement in the early stage and the pozzolanic reaction in the late stage. The pores of cement-fly ash are found to be filled with the hydration products, despite the presence of a mass of pores in the interior.

scholarly journals Enhanced Metakaolin Reactivity in Blended Cement with Additional Calcium Hydroxide

Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 367
Author(s):  
Kira Weise ◽  
Neven Ukrainczyk ◽  
Aaron Duncan ◽  
Eduardus Koenders
Keyword(s):  
Calcium Hydroxide ◽  
Blended Cement ◽  
Initial Mixture ◽  
Pozzolanic Reaction ◽  
Replacement Ratio ◽  
Pozzolanic Reactivity ◽  
Thermogravimetric Data ◽  
Binder Ratio ◽  
Water To Binder Ratio ◽  
Mass Balance Approach

This study aims to increase the pozzolanic reactivity of metakaolin (MK) in Portland cement (PC) blends by adding additional calcium hydroxide (CH_add) to the initial mixture. Cement paste samples were prepared with PC, MK and water with a water-to-binder ratio of 0.6. Cement replacement ratios were chosen from 5 to 40 wt.% MK. For higher replacement ratios, i.e., 20, 30 and 40 wt.% MK, CH_add was included in the mixture. CH_add-to-MK ratios of 0.1, 0.25 and 0.5 were investigated. Thermogravimetric analysis (TGA) was carried out to study the pozzolanic reactivity after 1, 7, 28 and 56 days of hydration. A modified mass balance approach was used to normalize thermogravimetric data and to calculate the calcium hydroxide (CH) consumption of samples with CH_add. Results showed that, without CH_add, a replacement ratio of 30 wt.% or higher results in the complete consumption of CH after 28 days at the latest. In these samples, the pozzolanic reaction of MK turned out to be restricted by the amount of CH available from the cement hydration. The increased amount of CH in the samples with CH_add resulted in an enhanced pozzolanic reaction of MK as confirmed by CH consumption measurements from TGA.

Hydration and strength evolution of air-cured zeolite-rich tuffs and siltstone blended cement pastes at low water-to-binder ratio

Clay Minerals ◽  
2015 ◽  
Vol 50 (1) ◽  
pp. 133-152 ◽  
Author(s):  
M.H. Cornejo ◽  
J. Elsen ◽  
C. Paredes ◽  
H. Baykara
Keyword(s):  
Compressive Strength ◽  
Blended Cement ◽  
Cementitious Materials ◽  
Pozzolanic Reaction ◽  
Supplementary Cementitious Materials ◽  
Experimental Conditions ◽  
Cement Pastes ◽  
Carbonation Reaction ◽  
Curing Conditions ◽  
Strength Evolution

AbstractThis contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ∼45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.

scholarly journals CO2 Uptake of Carbonation-Cured Cement Blended with Ground Volcanic Ash

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2187 ◽  
Author(s):  
Joon Seo ◽  
Issam Amr ◽  
Sol Park ◽  
Rami Bamagain ◽  
Bandar Fadhel ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Volcanic Ash ◽  
Blended Cement ◽  
Pozzolanic Reaction ◽  
Partial Replacement ◽  
Co2 Uptake ◽  
Supplementary Cementitious Material ◽  
Natural Minerals ◽  
The Matrix ◽  
Carbonation Curing

Accelerated carbonation curing (ACC) as well as partial replacement of cement with natural minerals are examples of many previous approaches, which aimed to produce cementitious products with better properties and environmental amicabilities. In this regard, the present study investigates CO2 uptake of carbonation-cured cement blended with ground Saudi Arabian volcanic ash (VA). Paste samples with cement replacement of 20%, 30%, 40%, and 50% by mass were prepared and carbonation-cured after initial curing of 24 h. A compressive strength test, X-ray diffractometry (XRD), and thermogravimetry were performed. Although pozzolanic reaction of VA hardly occurred, unlike other pozzolana in blended cement, the results revealed that incorporation of VA as a supplementary cementitious material significantly enhanced the compressive strength and diffusion of CO2 in the matrix. This increased the CO2 uptake capacity of cement, reducing the net CO2 emission upon carbonation curing.

scholarly journals Elucidation of the Hydration Reaction of UHPC Using the PONKCS Method

Materials ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 4661
Author(s):  
Hyunuk Kang ◽  
Nankyoung Lee ◽  
Juhyuk Moon
Keyword(s):  
Heat Treatment ◽  
Silica Fume ◽  
High Performance ◽  
High Performance Concrete ◽  
Structural Evolution ◽  
Pozzolanic Reaction ◽  
Hydration Reaction ◽  
Ultra High Performance Concrete ◽  
Degree Of Hydration ◽  
Amorphous Phases

This study explored the hydration reaction of ultra-high-performance concrete (UHPC) by using X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA) as analysis methods. The partial- or no-known crystal structure (PONKCS) method was adopted to quantify the two main amorphous phases of silica fume and C-S-H; such quantification is critical for understanding the hydration reaction of UHPC. The measured compressive strength was explained well by the degree of hydration found by the PONKCS method, particularly the amount of amorphous C-S-H. During heat treatment, the pozzolanic reaction was more intensified by efficiently consuming silica fume. After heat treatment, weak but continuous hydration was observed, in which the cement hydration reaction was dominant. Furthermore, the study discussed some limitations of using the PONKCS method for studying the complicated hydration assemblage of UHPC based on the results of TGA and NMR. Generally, the PONKCS method underestimated the content of silica fume in the early age of heat treatment. Furthermore, the structural evolution of C-S-H, confirmed by NMR, should be considered for more accurate quantification of C-S-H formed in UHPC. Nevertheless, PONKCS-based XRD could be useful for understanding and optimizing the material properties of UHPC undergoing heat treatment.

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