Preparation of MgO- and CaO-Bearing Expansive Agent Used for Cement-Based Materials

2013 ◽  
Vol 539 ◽  
pp. 211-214 ◽  
Author(s):  
Li Wu Mo ◽  
Yang Deng ◽  
An Qun Lu ◽  
Min Deng
Keyword(s):  
Cement Paste ◽  
Rapid Expansion ◽  
Curing Temperature ◽  
Cement Pastes ◽  
Expansive Agent ◽  
Mineral Phases ◽  
Mix Proportion ◽  
Cement Based Materials

Blended expansive agents consisting of MgO and CaO were prepared by calcining the mixtures of dolomite and magnesite. The mineral phases and microstructures of expansive agent were examined by XRD and SEM. The expansion properties of cement pastes containing 5% and 6% of expansive agent as well as the microstructure of hydrated expansive agent in cement paste were investigated. Results indicated that the contents of MgO and CaO in the blended expansive agent could be adjusted by changing the mix proportion of dolomite and magnesite. All the cement pastes containing expansive agent produced rapid expansion. At the same addition dosage, irrespective of curing temperature, expansive agent containing higher content of MgO produced greater expansion in cement pastes, particularly at late age, which probably ascribes to the relatively slow hydration of MgO.

Effect of Amount on Expansion Property of MgO-Type Expansive Agent Used in Cement-Based Materials

2011 ◽  
Vol 391-392 ◽  
pp. 803-806
Author(s):  
Zhi Bin Zhang ◽  
Ling Ling Xu ◽  
Fang Liu ◽  
Ming Shu Tang
Keyword(s):  
Cement Paste ◽  
Curing Temperature ◽  
Relative Invariant ◽  
Expansive Agent ◽  
Relative Expansion ◽  
Quantitative Effect ◽  
Expansion Property ◽  
Cement Based Materials ◽  
The Relationship ◽  
Curing Age

Previous research indicated that the expansion property of MgO-type expansive agent (MEA) strongly depended on the amount. However, the quantitative effect of amount on expansion property of MEA has not been clearly demonstrated. In the present the expansion value of cement paste with 3%, 4%, 5% and 6% MEA calcinated at 850°C and 1200 °C, and then relative expansion value was introduced to investigated the relationship between the mount and expansion of MEA. The results indicated The relative expansion of MEA calcinated at 850°C was relative invariant to curing temperature and proportional increased with the amount ratio. The relative expansion of MEA calcinated at 1200°C proportional increased with curing age, and the increasing rate rose with the amount ratio of MEA and curing temperature.

scholarly journals Effect of Calcium Nitrate on the Properties of Portland–Limestone Cement-Based Concrete Cured at Low Temperature

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1611
Author(s):  
Gintautas Skripkiūnas ◽  
Asta Kičaitė ◽  
Harald Justnes ◽  
Ina Pundienė
Keyword(s):  
Compressive Strength ◽  
Cement Paste ◽  
Setting Time ◽  
Calcium Nitrate ◽  
Curing Temperature ◽  
Hardened Concrete ◽  
Cement Pastes ◽  
Initial Setting Time ◽  
Initial Setting ◽  
Early Strength

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

scholarly journals CO2 Curing Efficiency for Cement Paste and Mortars Produced by a Low Water-to-Cement Ratio

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3883
Author(s):  
Seong Ho Han ◽  
Yubin Jun ◽  
Tae Yong Shin ◽  
Jae Hong Kim
Keyword(s):  
Cement Paste ◽  
Pressure Vessel ◽  
Gas Pressure ◽  
Strength Development ◽  
Co2 Uptake ◽  
Cement Pastes ◽  
Co2 Gas ◽  
Cement Ratio ◽  
Mix Proportion ◽  
Water To Cement Ratio

Curing by CO2 is a way to utilize CO2 to reduce greenhouse gas emissions. Placing early-age cement paste in a CO2 chamber or pressure vessel accelerates its strength development. Cement carbonation is attributed to the quickened strength development, and CO2 uptake can be quantitatively evaluated by measuring CO2 gas pressure loss in the pressure vessel. A decrease in CO2 gas pressure is observed with all cement pastes and mortar samples regardless of the mix proportion and the casting method; one method involves compacting a low water-to-cement ratio mix, and the other method comprises a normal mix consolidated in a mold. The efficiency of the CO2 curing is superior when a 20% concentration of CO2 gas is supplied at a relative humidity of 75%. CO2 uptake in specimens with the same CO2 curing condition is different for each specimen size. As the specimen scale is larger, the depth of carbonation is smaller. Incorporating colloidal silica enhances the carbonation as well as the hydration of cement, which results in contributing to the increase in the 28-day strength.

The relation between porosity, microstructure and strength, and the approach to advanced cement-based materials

1983 ◽  
Vol 310 (1511) ◽  
pp. 139-153 ◽  
Keyword(s):  
Elastic Modulus ◽  
Fracture Energy ◽  
Cement Paste ◽  
Compression Strength ◽  
Bending Strength ◽  
Cement Pastes ◽  
Cement Based Materials ◽  
Mdf Cements

A theory is formulated to connect the strength of cement paste with its porosity. The theory shows that bending strength is largely dictated by the length of the largest pores, as in the Griffith (1920) model, but there is also an influence of the volume of porosity, which affects toughness through changing elastic modulus and fracture energy. Verification of this theory was achieved by observing the large pores in cement, and then relating bending strength to the measured defect length, modulus and fracture energy. The argument was proved by developing processes to remove the large pores from cement pastes, thereby raising the bending strength to 70 MPa. Further removal of colloidal pores gave a bending strength of 150 MPa and compression strength up to 300 MPa with improved toughness. Re-introduction of controlled pores into these macro-defect-free (mdf) cements allowed Feret’s law (1897) to be explained.

Quantitative Characterization of Hydration of Cement Pastes by Rietveld Phase Analysis and Thermoanalysis

2013 ◽  
Vol 539 ◽  
pp. 19-24 ◽  
Author(s):  
Yong Qi Wei ◽  
Wu Yao
Keyword(s):  
Phase Analysis ◽  
Cement Paste ◽  
Rietveld Method ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Quantitative Characterization ◽  
Cement Pastes ◽  
Hydration Mechanism ◽  
Spot Check

The quantitative characterization of hydration of cement pastes has always been one of focuses of researchers’ attention. Rietveld phase analysis (RPA), a combination of quantitative X-ray diffraction (QXRD) and the Rietveld method, supplies a tool of an enormous potential for that. Although a few of related researches were conducted by RPA, the reported attention was not paid to the neat cement paste with a low w/c ratio. Therefore, this work aimed at the quantitative study on hydration of such a cement paste chiefly by this method, meanwhile, cooperated with the hyphenated technique of thermogravimetry with differential scanning calorimetry (TG-DSC), as a spot check. Results indicated that RPA was a reliable method in quantitatively characterizing hydration of cement pastes, and gave a clear decription of evolution of all main crystal phases in cement pastes; and that the evolution of monosulphate(Afm_12) was also able to be tracked quantitatively. This will help to understand better the hydration mechanism of cement pastes, as well as to investigate quantitatively effects of mineral and chemical admixtures on hydration of composite cementitious systems.

The Influence of Various Gypsum Dosage, Specific Area of Cement and Water Reducers on Bleeding of Fresh Cement Paste Using Low-Field NMR

2021 ◽  
Vol 1036 ◽  
pp. 255-262
Author(s):  
Yan Liang Ji ◽  
Zhen Ping Sun ◽  
Min Pang
Keyword(s):  
Cement Paste ◽  
Specific Area ◽  
High Water ◽  
Low Permeability ◽  
Cement Pastes ◽  
Bleeding Rate ◽  
Low Field ◽  
Low Field Nmr ◽  
Type Water ◽  
Hot Zone

Based on the low-field NMR, this study inveitigated bleeding property of the fresh cement pastes mixed with various gypsum dosage, specific area of cement and water reducers. Results showed that the gypsum dosage between 3 % and 5 % will cause an decrease bleeding and a lower bleeding velocity, while a 1 % gypsum dosage will increase the bleeding as a function of time. The increase of the cement surface will lead to a less bleeding rate. This can be explained that the finer particle will contribute to the packing which will form a low permeability of the cement paste, as a result less bleeding water is observed. The PCEs-made sample has smaller hot zone area which indocated the PCEs has good bleeding stability when varing water cement ratio. Furthermore, bying comparing with the NPE, it was found the ACS type water reducer has higher bleeding sensitivity when high water cement ratios were used.

Interaction Between Naphthalene Sulfonate and Silica Fume in Portland Cement Pastes

1987 ◽  
Vol 114 ◽  
Author(s):  
Sidney Diamond ◽  
Leslie J. Struble
Keyword(s):  
Portland Cement ◽  
Silica Fume ◽  
Cement Paste ◽  
Uv Spectrophotometry ◽  
Residual Concentration ◽  
Cement Pastes ◽  
High Ph ◽  
Substantial Concentration ◽  
Low Dosage

ABSTRACTPortland cement pastes were mixed with predissolved naphthalene sulfonate superplasticizer at normal water:cement ratios. Solutions were separated from the fresh pastes at intervals and the residual concentration of the superplasticizer determined by UV spectrophotometry. At low dosage levels essentially all of the superplasticizer was found to be removed from solution within a few minutes; at high dosage levels a substantial concentration was maintained in solution at least to approximately the time of set. In pastes in which silica fume replaced 10% by weight of the cement, it was found that the incorporation of silica fume significantly increased the uptake of superplasticizer. In separate trials it was found that the silica fume by itself adsorbed little superplasticizer, even from high pH solution simulating that of cement paste.

Study of the pozzolanic activity and hydration products of cement pastes with addition of natural zeolites

Clay Minerals ◽  
2011 ◽  
Vol 46 (2) ◽  
pp. 241-250 ◽  
Author(s):  
V. Lilkov ◽  
O. Petrov ◽  
V. Petkova ◽  
N. Petrova ◽  
Y. Tzvetanova
Keyword(s):  
Surface Area ◽  
Cement Paste ◽  
Chemical Reactions ◽  
Natural Zeolite ◽  
Early Stage ◽  
Pozzolanic Activity ◽  
Large Surface Area ◽  
Natural Zeolites ◽  
Hydration Products ◽  
Cement Pastes

AbstractThis paper presents results from comparative thermogravimetric, calorimetric and pozzolanic activity analyses of five natural zeolite samples from Bulgaria, Slovakia, Philippines, USA and North Korea. The zeolites actively participate in the hydration processes of cement. Their activity in the early stage of hydration is based mainly on the large surface area of the particles while, in the later stages of activation, chemical reactions occur between the products of the hydration of cement and the soluble SiO2 that is present in the bulk of the zeolites. It has been shown that in all cement pastes which contain zeolite additives, the quantity of portlandite is lower than that in pure cement paste or is even totally absent. The amounts of hydration products are greater when 30% zeolite is used than when 10% zeolite is added (excluding the sample with chabazite). The lowest pozzolanic activity is shown by chabazite, which possessed the lowest SiO2/Al2O2 ratio.

Test Methods for Rheological Properties of Self-Compacting Concrete Pastes

2011 ◽  
Vol 338 ◽  
pp. 396-400
Author(s):  
Bao Guo Ma ◽  
Hui Xian Wang ◽  
Jian Huang ◽  
Liu Qing Song
Keyword(s):  
Rheological Properties ◽  
Cement Paste ◽  
Test Methods ◽  
General Study ◽  
Self Compacting Concrete ◽  
Cement Pastes ◽  
Different Types ◽  
Over Time

This paper provides a general study on cement paste flow which derived from self- compacting concretes. Rheometer, Marsh cone and mini-slump cone were used to evaluate fluidity of cement pastes containing superplasticizers of different types and dosages and loss of fluidity over time. There is a superplasticizer saturation dosage beyond which no significant fluidity increase can be found. This paper evaluated the effect of these three methods using rheometer as control and the optimum superplasticizer type for the preparation of self-compacting concrete was suggested.

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