scholarly journals Influence of Different Alkali Sulfates on the Shrinkage, Hydration, Pore Structure, Fractal Dimension and Microstructure of Low-Heat Portland Cement, Medium-Heat Portland Cement and Ordinary Portland Cement

2021 ◽  
Vol 5 (3) ◽  
pp. 79
Author(s):  
Yang Li ◽  
Hui Zhang ◽  
Minghui Huang ◽  
Haibo Yin ◽  
Ke Jiang ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Portland Cement ◽  
Pore Structure ◽  
Ordinary Portland Cement ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Crystal Forms ◽  
Pore Structures ◽  
Cement Based Materials ◽  
Mineral Compositions

In cement-based materials, alkalis mainly exist in the form of different alkali sulfates. In this study, the impacts of different alkali sulfates on the shrinkage, hydration, pore structure, fractal dimension and microstructure of low-heat Portland cement (LHPC), medium-heat Portland cement (MHPC) and ordinary Portland cement (OPC) are investigated. The results indicate that alkali sulfates magnify the autogenous shrinkage and drying shrinkage of cement-based materials with different mineral compositions, which are mainly related to different pore structures and hydration processes. LHPC has the lowest shrinkage. Otherwise, the effect of alkali sulfates on the autogenous shrinkage is more profound than that of drying shrinkage. Compared with the pore size distribution, the fractal dimension can better characterize the shrinkage properties of cement-based materials. It is noted that the contribution of K2SO4 (K alkali) to the promotion effect of shrinkage on cement-based materials is more significant than that of Na2SO4 (Na alkali), which cannot be ignored. The microstructure investigation of different cement-based materials by means of nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) shows that this effect may be related to the different pore structures, crystal forms and morphologies of hydration products of cement-based materials.

scholarly journals Influence of MgO on the Hydration and Shrinkage Behavior of Low Heat Portland Cement-Based Materials via Pore Structural and Fractal Analysis

2022 ◽  
Vol 6 (1) ◽  
pp. 40
Author(s):  
Lei Wang ◽  
Xiao Lu ◽  
Lisheng Liu ◽  
Jie Xiao ◽  
Ge Zhang ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Portland Cement ◽  
Pore Structure ◽  
Fractal Analysis ◽  
Concrete Structures ◽  
Mass Concrete ◽  
Pore Structures ◽  
Cement Based Materials ◽  
Induction Stage ◽  
Shrinkage Behavior

Currently, low heat Portland (LHP) cement is widely used in mass concrete structures. The magnesia expansion agent (MgO) can be adopted to reduce the shrinkage of conventional Portland cement-based materials, but very few studies can be found that investigate the influence of MgO on the properties of LHP cement-based materials. In this study, the influences of two types of MgO on the hydration, as well as the shrinkage behavior of LHP cement-based materials, were studied via pore structural and fractal analysis. The results indicate: (1) The addition of reactive MgO (with a reactivity of 50 s and shortened as M50 thereafter) not only extends the induction stage of LHP cement by about 1–2 h, but also slightly increases the hydration heat. In contrast, the addition of weak reactive MgO (with a reactivity of 300 s and shortened as M300 thereafter) could not prolong the induction stage of LHP cement. (2) The addition of 4 wt.%–8 wt.% MgO (by weight of binder) lowers the mechanical property of LHP concrete. Higher dosages of MgO and stronger reactivity lead to a larger reduction in mechanical properties at all of the hydration times studied. M300 favors the strength improvement of LHP concrete at later ages. (3) M50 effectively compensates the shrinkage of LHP concrete at a much earlier time than M300, whereas M300 compensates the long-term shrinkage more effectively than M50. Thus, M300 with an optimal dosage of 8 wt.% is suggested to be applied in mass LHP concrete structures. (4) The addition of M50 obviously refines the pore structures of LHP concrete at 7 days, whereas M300 starts to refine the pore structure at around 60 days. At 360 days, the concretes containing M300 exhibits much finer pore structures than those containing M50. (5) Fractal dimension is closely correlated with the pore structure of LHP concrete. Both pore structure and fractal dimension exhibit weak (or no) correlations with shrinkage of LHP concrete.

Study on the Influence of Air-Entraining Agent on the Impermeability of Cement-Based Composites Based on its Pore Structure by Fractal Theory

2010 ◽  
Vol 168-170 ◽  
pp. 615-618
Author(s):  
Zhi Qin Du ◽  
Wei Sun
Keyword(s):  
Fractal Dimension ◽  
Pore Structure ◽  
Mercury Intrusion Porosimetry ◽  
Fractal Theory ◽  
Mercury Intrusion ◽  
Pore Structures ◽  
Cement Based Materials

The effect of different quantity of air-entraining agent on the impermeability of cement-based materials are studied in this paper. Impermeability test and mercury intrusion porosimetry (MIP) method were used to characterize the impermeability and pore structures. The fractal dimension is used to describe the characteristic of pore structure and calculated by the data of MIP experiment. The result shows that owing to the improvement of pore structure, the impermeability performance of the cement-based composites is noticeably enhanced when air-entraining agent is added with appropriate quantity.

scholarly journals Autogenous and drying shrinkage of mortars based on Portland and calcium sulfoaluminate cements

2020 ◽  
Vol 53 (5) ◽  
Author(s):  
Davide Sirtoli ◽  
Mateusz Wyrzykowski ◽  
Paolo Riva ◽  
Pietro Lura
Keyword(s):  
Portland Cement ◽  
Water Demand ◽  
Ordinary Portland Cement ◽  
Rapid Evolution ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
High Water ◽  
Early Age ◽  
Volume Changes ◽  
Calcium Sulfoaluminate

Abstract Calcium sulfoaluminate (CSA) cement can be used as an alternative binder in concrete, partially or fully replacing ordinary Portland cement. While CSA cement considerably accelerates the mechanical properties development, the rapid evolution of the microstructure together with the high water demand cause rapid and large volume changes at early ages. As volume changes may lead to early-age cracking, measures to reduce them may be required In this paper, autogenous and drying shrinkage are studied in mortars prepared with Portland cement, CSA cement or a 50/50 blend as binder. Very fast self-desiccation and high autogenous shrinkage of the CSA-based mortar were observed compared to the mortar made with Portland cement. On the other hand, the early-age volume changes can be limited if a blend of the two cements is used. The blended system revealed a bi-modal trend in the evolution of self-desiccation and autogenous shrinkage, in which the initial fast self-desiccation and shrinkage enter the dormant phase after the first couple of days and again start after about 28 days.

Characterization of Micro-Pore Structure in Novel Cement Matrices

2014 ◽  
Vol 1712 ◽  
Author(s):  
Seyoon Yoon ◽  
Isabel Galan ◽  
Kemal Celik ◽  
Fredrik P. Glasser ◽  
Mohammed S. Imbabi
Keyword(s):  
Portland Cement ◽  
Pore Structure ◽  
Engineering Properties ◽  
Calcium Sulfoaluminate ◽  
Pore Structures ◽  
Porosity And Permeability ◽  
Experimental Protocols ◽  
Novel Processing ◽  
Main Component

ABSTRACTCalcium sulfoaluminate (CSA) cements are being developed using a novel processing method having as its objective lowering specific CO2 emissions by ∼50% relative to a Portland cement benchmark. We need to be able to measure the properties of the products. Porosity and permeability measurements help define the engineering properties but their quantification is influenced by the choice of experimental protocols. In the present study we used ordinary Portland cement (PC) paste as a benchmark and hydrated ye’elimite, which is a main component of CSA cements, to understand its pore structure. We report on the use of synchrotron-sourced radiation for µCT (Computerized Tomography) and 3D image re-construction of the internal micro-pore structure of PC and ye’elimite-gypsum pastes. As a comparison, porosity and permeability measurements were traditionally obtained using Mercury Intrusion Porosimetry (MIP). The Mori-Tanaka method and the polynomial statistical model were used to analyze the effects of different 3-D micro-pore structures on mechanical properties. The results show that e micro-pore structures differ considerably between PC and ye’elimite pastes and their bulk modulus is significantly affected by the shapes of their micro-pore structures.

EXPLORATORY STUDY ON THE MECHANICAL AND PHYSICAL PROPERTIES OF CONCRETE CONTAINING SULFUR

2015 ◽  
Vol 77 (32) ◽  
Author(s):  
David Yeoh ◽  
Koh Heng Boon ◽  
Norwati Jamaluddin
Keyword(s):  
Portland Cement ◽  
Physical Properties ◽  
Ordinary Portland Cement ◽  
Cement Content ◽  
Drying Shrinkage ◽  
Portland Cement Concrete ◽  
Cement Concrete ◽  
Complete Replacement ◽  
Mechanical And Physical Properties ◽  
Ordinary Portland Cement Concrete

This research is an exploratory experiment into sulfur concrete used not as a complete replacement of cement but as an additional material in percentage of the cement content. The aim of this research was to explore the possible appreciation of mechanical and physical properties of concrete containing sulfur with percentages of 1%, 5% and 10% of the cement content. The sulfur used here was not heat-activated, hence the binding effect in sulfur was absent. The experimental results revealed that concrete containing sulfur did not perform better in their strength properties, both compressive strength and flexural strength. The physical properties such as water penetration and water absorption for concrete containing sulfur also showed poor performance in comparison to ordinary Portland cement concrete. Such phenomena are very likely due to the sulfur not being activated by heat. Carbonation test did not show good results as a longer term of testing is required. Drying shrinkage property was found to be encouraging in that concrete containing 10% sulfur had quite significant reduction in drying shrinkage as opposed to ordinary Portland cement concrete. 

scholarly journals Fractal analysis of pore structures in graphene oxide-carbon nanotube based cementitious pastes under different ultrasonication

2019 ◽  
Vol 8 (1) ◽  
pp. 107-115 ◽  
Author(s):  
Yuan Gao ◽  
Hongwen Jing ◽  
Zefu Zhou
Keyword(s):  
Graphene Oxide ◽  
Fractal Dimension ◽  
Pore Structure ◽  
Pore Size ◽  
Size Range ◽  
Fractal Dimensions ◽  
Pore Characteristics ◽  
Pore Structures ◽  
Cement Additive ◽  
Multi Walled Carbon Nanotubes

Abstract Nano cement additive using a hybrid of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) combines the excellent affinity of GO and the superior mechanical properties of MWCNTs. Ultrasonication is the key process to disperse the GO/MWCNTs and further optimizes the pore structures of cement-based pastes. Fractal dimension can effectively and quantitatively characterize the pore structures of cementitious composites. The present study investigates the fractal dimensions of pore structures of GO/MWCNT-OPC pastes under power- and time-controlled ultrasonication based on the mercury intrusion porosimetry (MIP) tests data. The finding of this study shows that comparing to calculating the fractal dimension of the overall pore size range, assessing the variations of fractal dimension of individual pore size range is more effective in evaluating the pore characteristic. The fractal dimension of larger capillary pores $$\left( {{D}_{>{{10}^{4}}nm}} \right)$$can be use to describe the change of pore structure of GO/MWCNT-OPC pastes under ultrasonication treatment with sufficient accuracy as higher value of $${{D}_{>{{10}^{4}}nm}}$$indicates better pore characteristics. The fractal dimension change trend of mesopores is always opposite to that of bigger capillary pores. Modest increment in both power- and time-controlled ultrasonication seems to result in the increase of the fractal dimension of capillary pores and lead to better reinforcement effects. Prolongation of ultrasonication time slightly influences the pore structure of the specimens, while nano cement additives exposed to excess ultrasonication power fail to afford adequate reinforcing effect and finally cause the deterioration of the pore structures. The findings of this study can provide helpful information of GO/MWCNT-OPC pastes and ultrasonication treatment in the future.

scholarly journals On effect of superplasticizers and mineral additives on shrinkage of hardened cement paste and concrete

2018 ◽  
Vol 196 ◽  
pp. 04018 ◽  
Author(s):  
Grigory Nesvetaev ◽  
Yulia Koryanova ◽  
Tatiana Zhilnikova
Keyword(s):  
Portland Cement ◽  
Cement Paste ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Hardened Cement ◽  
Portland Cement Concrete ◽  
Cement Concrete ◽  
Hardened Cement Paste ◽  
Mineral Additive ◽  
Mineral Additives

A model describing the variation in autogenous shrinkage and drying shrinkage of portland cement concrete, depending on the volume of aggregates and the shrinkage of hardened cement paste, is presented. The equation to calculate shrinkage of concrete as a function of the volume of aggregates and shrinkage of a hardened cement paste was proposed. Formulas are proposed that describe the change in the shrinkage of hardened cement paste as a function of water/cement. The results of studies of the effect of superplasticizers and mineral additives on the autogenous shrinkage and the drying shrinkage of hardened cement paste are presented. Concretes made with superplasticizer and mineral additive may have the potential lower the value of drying shrinkage. The shrinkage value can be lowered from 30% till 70%. Concretes containing superplasticizers and mineral additives can potentially have the autogenous shrinkage reduced to 75%, or increased to 180%.

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