Hydration properties of cement pastes containing high-volume mineral admixtures

Chao-Wei Tang 사단법인 한국계산역학회 2010 Computers and Concrete, An International Journal Vol.7 No.1

This research aimed to investigate the influence of high-volume mineral admixtures (MAs), i.e., fly ash and slag, on the hydration characteristics and microstructures of cement pastes. Degree of cement hydration was quantified by the loss-on-ignition technique and degree of pozzolanic reaction was determined by a selective dissolution method. The influence of MAs on the pore structure of paste was measured by mercury intrusion porosimetry. The results showed that the hydration properties of the blended pastes were a function of water to binder ratio, cement replacement level by MAs, and curing age. Pastes containing fly ash exhibited strongly reduced early strength, especially for mix with 45% fly ash. Moreover, at a similar cement replacement level, slag incorporated cement paste showed higher degrees of cement hydration and pozzolanic reaction than that of fly ash incorporated cement paste. Thus, the present study demonstrates that high substitution rates of slag for cement result in better effects on the short- and long-term hydration properties of cement pastes.

Hybrid-ANFIS approaches for compressive strength prediction of cementitious mortar and paste employing magnetic water

Mosbeh R. Kaloop,Omar M.M. Yousry,Pijush Samui,Mohamed M.Y. Elshikh,Jong Wan Hu 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.4

The compressive strength is an important mechanical feature of concrete that is needed in construction design. Thus, a lot of investigations were carried out to predict the compressive strength of various concretes. However, the prediction models for the compressive strength of cement mortar or paste that include magnetic water (MW) and granulated blast-furnace slag (GBFS) are still limited. The current study has developed hybrid algorithms based on adaptive neuro-fuzzy inference system (ANFIS) for modeling the compressive strength of cement mortar and paste that made with MW and GBFS as a novel mixture content. A total of 144 experimental sets of concrete-compressive strength tests for each cement mortar and paste were collected to train and validate the proposed methods, in which the cycles number of water magnetization, cement, GBFS, superplasticizer contents and curing time are set as the input data while the compressive strength value is set as the output. The developed hybrid algorithms of ANFIS optimized by firefly algorithm (FA), Improved Particle Swarm Optimization (IPSO) and biogeographybased optimization (BBO) algorithms for predicting the compressive strength of the mortar and paste. The proposed models and relevance vector machine (RVM) approach were evaluated and compared. The results showed that the ANFIS-FA outperforms other models for modeling the compressive strength of cement mortar and paste. The adjusted-coefficient of determination and root mean square error values of cement mortar models (96.20%, 92.33%, 92.36% and 89.41%) and (2.17 MPa, 3.10 MPa, 3.18 MPa and 3.06 MPa) and of cement paste models (96.92%, 80.91%, 92.19% and 88.18%) and (2.45 MPa, 5.80 MPa, 4.39 MPa and 5.20 MPa) were determined for ANFIS-FA, ANFIS-IPSO, ANFIS-BBO and RVM models, respectively, which indicate that the ANFIS-FA is a suitable model for estimating the compressive strength of cement mortar and paste that include MW. Moreover, the sensitivity of MW and GBFS is shown high for modeling the compressive strength of cement mortar.

Issues on characterization of cement paste microstructures from μ -CT and virtual experiment framework for evaluating mechanical properties

Kim, Ji-Su,Chung, Sang-Yeop,Stephan, Dietmar,Han, Tong-Seok Elsevier 2019 Construction and Building Materials Vol.202 No.-

<P><B>Abstract</B></P> <P>There are issues on the microstructure characterization of cement paste obtained from μ -CT due to resolution limits, and evaluation of properties through virtual experiments. A phase separation procedure between the solid and pore phases, which can be used for pure cement paste microstructures, is proposed. The problems of underestimation of microstructural characteristics such as porosity in virtual specimens from μ -CT, as compared to real specimens, are addressed. Reflecting such underestimation, the process of input modeling parameter determination for virtual experiments on mechanical property evaluation using the phase field fracture model is elaborated. Through virtual tests, the effects of domain size and mesh resolution on the evaluated properties are investigated, and the correlation between the microstructural characterization parameters and mechanical properties is reconfirmed. It is shown that the virtual experiment framework proposed in this study can be used as a loading tool to supplement time and effort consuming real experiments for evaluating the mechanical properties of cement paste at the micro-scale.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Issues on domain size and resolution of μ-CT images of cement paste are identified. </LI> <LI> Phase separation procedure for μ-CT images of cement paste is extended. </LI> <LI> Phase field fracture model performs adequately as a virtual loading tool. </LI> <LI> Virtual experiment shows a potential to supplement real experiment of cement paste. </LI> </UL> </P>

Hydration of Ultrafine and Ordinary Portland Cement at Early Ages

Xudong Chen,Jikai Zhou,Yuanyuan Yan 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.6

Experimental results of a quantitative of the hydration of ultrafine and ordinary Portland cement pastes were presented in thispaper. The degree of hydration of cement pastes was determined based on the determination of non-evaporable content. The purposeof this study was to explore the mechanism of the effects of particle size distribution on hydration kinetics of cement. The dataobtained from test indicate that at each age before 7 days, the non-evaporable water content of the ultrafine cement paste was higherthan that of the ordinary cement paste. The fineness has a great effect on early 7 days hydration. In the later age, the rate of hydrationslows down and diffusion of silicate ions through layers of existing products becomes the rate-limiting process. The porosity ofultrafine cement paste is lower thod than of ordinary cement paste. The difference in porosity of two cement paste is mostpronounced at early ages before 14 days. A general reduction in porosity with increasing in age is observed from test results. Theultrafine cement consistently produces higher gel/space ratios at all seven testing ages. At an age of 1 day, the ordinary Portlandcement achieves 79% of its fine counterpart.

Effect of Graphene Oxide on Chemical Shrinkage Behavior of Cement-Based Composite Paste

Yanchun Miao,Yu Zhang,Beibei Li,Leilei Chai,Gang Ma 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.4

As a new type of nano carbon material, graphene oxide (GO) has attracted extensive attention in the academic field over recent years due to its abundant oxygen-containing functional groups and large specific surface area, which can improve the microstructure and mechanical properties of cement-based materials. However, the effect of GO on the chemical shrinkage of cement-based materials remains unclear. Therefore, in this study, to reveal the chemical shrinkage characteristics of GO/cement composite paste (GO/CP), the chemical shrinkage of cement-based composite paste with different water/cement ratios (0.32, 0.42, and 0.52), different mass fractions of GO (0 wt%, 0.01 wt%, 0.03 wt%, and 0.05 wt%), and different mass fractions of polycarboxylate superplasticizer (PC) (0 wt%, 0.02 wt%, and 0.03 wt%) were measured using the volumetric method. The results showed that the chemical shrinkage of GO/CP increases significantly with the increasing water/cement ratio. The addition of PC appeared to compound GO/CP chemical shrinkage, showing a trend of first augmenting and then reducing with the increasing PC content. For the same water/cement ratio, the chemical shrinkage of the GO/CP specimen was lower than that of the normal cement paste (NCP). When the GO content reached the range of 0.03 wt% – 0.05 wt%, the shrinkage value reached the minimum; and when the water/cement ratio was 0.42, the growth rate of chemical shrinkage of the GO/CP specimen in the middle and late hydration processes was significantly larger than that of NCP. The analysis revealed that the regulating effect of GO on cement-based materials is mainly reflected in the refinement of the pore structure and bonding behavior of the hydration product Ca(OH)2. In addition, to determine the influence of GO and PC on chemical shrinkage of GO/CP, the existing model for chemical shrinkage of NCP was modified and the functions K(ξ, t) and P(λ, t) were introduced as impact parameters, after which a suitable prediction model for chemical shrinkage of GO/CP was established by curve fitting. This study provides a theoretical basis for improving the performance of cement-based materials and clarifying the function mechanism of GO.

Premature Stiffening of Cement Paste Caused by Secondary Gypsum and Syngenite Formation (False Set)

Chung, Chul-Woo,Lee, Jae-Yong Architectural Institute of Korea 2011 Architectural research Vol.13 No.1

The purpose of this research is to investigate the effect of specific hydration reaction on the stiffening process of cement paste. The cement compositions are manipulated to cause specific hydration reactions (secondary gypsum and syngenite formation) responsible for false set, and the relationship between specific hydration reactions and the flow and stiffening behavior of cement paste were investigated using modified ASTM C 403 penetration resistance measurement and oscillatory shear rheology. X-ray powder diffraction (XRD) was used for the phase identification associated with premature stiffening of cement paste. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were used for verification of syngenite formation. From the results, both secondary gypsum and syngenite formation caused faster stiffening and set. The amount of syngenite produced during 1 hour hydration was approximately 1 % of total mass of the cement paste, but cement paste with syngenite formation showed significantly accelerated stiffening behavior compared to normal cement paste.

Premature Stiffening of Cement Paste Caused by Secondary Gypsum and Syngenite Formation (False Set)

Chul-Woo Chung,Jae-Yong Lee 대한건축학회 2011 Architectural research Vol.13 No.1

The purpose of this research is to investigate the effect of specific hydration reaction on the stiffening process of cement paste. The cement compositions are manipulated to cause specific hydration reactions (secondary gypsum and syngenite formation) responsible for false set, and the relationship between specific hydration reactions and the flow and stiffening behavior of cement paste were investigated using modified ASTM C 403 penetration resistance measurement and oscillatory shear rheology. X-ray powder diffraction (XRD) was used for the phase identification associated with premature stiffening of cement paste. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were used for verification of syngenite formation. From the results, both secondary gypsum and syngenite formation caused faster stiffening and set. The amount of syngenite produced during 1 hour hydration was approximately 1 % of total mass of the cement paste, but cement paste with syngenite formation showed significantly accelerated stiffening behavior compared to normal cement paste.

XRF (X-ray fluorescence)를 활용한 고온환경에 노출된 시멘트 페이스트 분석의 이해

전길송,허영선 한국구조물진단유지관리공학회 2023 한국구조물진단유지관리공학회 논문집 Vol.27 No.6

By using XRF (X-ray fluorescence), this study investigates the variation of chemical properties in cement pastes at elevated temperatures. High-temperature conditions were prepared by using an electric furnace, planning a total of 11 target temperatures ranging from room temperature to 1000 ℃. A standard library of geo-quant basic was applied for the analysis of 12 elements in cement paste, including Ca, Si, Al, Fe, S, Mg, Ti, Sr, P, Mn, Zn and K. The results revealed that, as the temperature increased, the proportion of each element in the cement paste also increased. With the exception of a few elements present in extremely low amounts in the cement pastes, the variation in the composition ratio of most elements exhibited a strong correlation with temperature, with an R-squared value exceeding 0.98. In this study, cement pastes exposed to normal and high-temperature environments were compared. The authors established that the reasons for the different results in this comparison can be explained from the same perspective as when comparing raw cement with cement paste. Furthermore, this study discussed the potentially most dominant parameter when investigating the properties of cement paste using XRF.

Strength Gain Mechanisms of Blended-Cements Containing Marble Powder and Brick Powder

Mehmet Serkan Kirgiz 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1

Strength gain mechanisms of blended-cements containing marble powder and brick powder were investigated in the presence ofchemical composition changings of cement pastes. Blended Cements (BC) were prepared blending of 5% gypsum and 6%, 20%,21% and 35% Marble Powder (MP) or 6%, 20%, 21% and 35% Brick Powder (BP) for CEMI42.5N cement clinker and grindingthese portions in ball mill at 30 (min). Pastes and mortars were also drawn up with these cements. Chemical compositions of pastes,Compressive Strength (CS) and Flexural Strength (FS) of mortars were determined at 7th-day, 28th-day and 90th-day according asstandard methods. Experimental results indicated that fluctuation of SiO2, Na2O and alkali at Marble Powder-Blended Cement Paste(MP-BCP) and continuously increasing of SiO2 at Brick Powder-Blended Cement Paste (BP-BCP) positively induced strength gainmechanism of BCM since MP up to 6% or BP up to 35% were blended for cement.

Premature Stiffening of Cement Paste Caused by Secondary Gypsum and Syngenite Formation (False Set)

정철우,이재용 대한건축학회 2011 Architectural research Vol.13 No.1

The purpose of this research is to investigate the effect of specific hydration reaction on the stiffening process of cement paste. The cement compositions are manipulated to cause specific hydration reactions (secondary gypsum and syngenite formation) responsible for false set, and the relationship between specific hydration reactions and the flow and stiffening behavior of cement paste were investigated using modified ASTM C403 penetration resistance measurement and oscillatory shear rheology. X-ray powder diffraction (XRD) was used for the phase identification associated with premature stiffening of cement paste. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA)were used for verification of syngenite formation. From the results, both secondary gypsum and syngenite formation caused faster stiffening and set. The amount of syngenite produced during 1 hour hydration was approximately 1 % of total mass of the cement paste, but cement paste with syngenite formation showed significantly accelerated stiffening behavior compared to normal cement paste.