scholarly journals A Mathematical Model for the Electrical Resistivity of Cement Paste at Early Ages Considering the Partially Saturated State

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3306 ◽  
Author(s):  
Ye Tian ◽  
Xin Xu ◽  
Haodong Ji ◽  
Zushi Tian ◽  
Xianyu Jin ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Electrical Resistivity ◽  
Cement Paste ◽  
Isothermal Calorimetry ◽  
Setting Time ◽  
Degree Of Saturation ◽  
Early Age ◽  
Saturation State ◽  
Partially Saturated ◽  
Saturated State

For cementitious materials, electrical resistivity is often used in the study of the cement hydration process at early age, as one of the few indicators that can be continuously and non-destructively monitored. Variation characteristics of resistivity are widely reported to interact with the early-age performance of cement paste, such as hydration kinetics parameters and setting time. However, there is no reasonable mathematical model to predict the resistivity at early ages, especially within the first 24 h, due to significant changes in the porosity and degree of saturation. In this work, a mathematical model was developed by considering the partially saturated state and density change of C-S-H (calcium silicate hydrate). To verify the model, two experimental methods were chosen, including the non-contact electrical resistivity test and isothermal calorimetry test. The hydration heat and resistivity of cement paste with a water–cement ratio of 0.35 and 0.45 were continuously monitored for 3 days. In the resistivity test, embedded temperature sensors were used to monitor the internal temperature and temperature correction was treated carefully in order to obtain accurate data. The test results prove that the mathematical model can accurately predict electrical resistivity and describe the saturation state of early-age cement pastes under sealed curing.

scholarly journals Effects of Highly Crystalized Nano C-S-H Particles on Performances of Portland Cement Paste and Its Mechanism

Crystals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 816
Author(s):  
Yuli Wang ◽  
Huijuan Lu ◽  
Junjie Wang ◽  
Hang He
Keyword(s):  
Portland Cement ◽  
Cement Paste ◽  
Setting Time ◽  
Tricalcium Silicate ◽  
Strength Development ◽  
Early Age ◽  
Hydration Products ◽  
X Ray ◽  
Early Strength ◽  
Portland Cement Paste

In order to improve the early age strength of ordinary Portland cement-based materials, many early strength agents were applied in different conditions. Different from previous research, the nano calcium silicate hydrate (C-S-H) particles used in this study were synthesized through the chemical reaction of CaO, SiO2, and H2O under 120 °C using the hydrothermal method, and the prepared nano C-S-H particles were highly crystalized. The influences of different amounts of nano C-S-H particles (0%, 0.5%, 1%, 2% and 3% by weight of cement) on the setting time, compressive strength, and hydration heat of cement paste were studied. The hydration products and microstructure of the cement paste with different additions of nano C-S-H particles were investigated through thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), and scanning electron microscope (SEM) tests. The results show that the nano C-S-H particles could be used as an early strength agent, and the early strength of cement paste can be increased by up to 43% through accelerating the hydration of tricalcium silicate (C3S). However, the addition of more than 2% nano C-S-H particles was unfavorable to the later strength development due to more space being left during the initial accelerated hydration process. It is suggested that the suitable content of the nano C-S-H particles is 0.5%−1% by weight of cement.

scholarly journals Effects of graphene oxide on early-age hydration and electrical resistivity of Portland cement paste

2017 ◽  
Vol 136 ◽  
pp. 506-514 ◽  
Author(s):  
Wengui Li ◽  
Xiangyu Li ◽  
Shu Jian Chen ◽  
Yan Ming Liu ◽  
Wen Hui Duan ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Graphene Oxide ◽  
Portland Cement ◽  
Cement Paste ◽  
Early Age ◽  
Portland Cement Paste ◽  
Early Age Hydration

Effect of Carboxylmethyl Cellulose Sulfate (CMC-S) on the Hydration Process of Cement Paste

2013 ◽  
Vol 838-841 ◽  
pp. 123-126
Author(s):  
Feng Yuan Huang ◽  
Xiao Jie Wu ◽  
Wei Feng Ying ◽  
Yong Peng Yu ◽  
Hong Xun Chi
Keyword(s):  
Cement Paste ◽  
Differential Scanning Calorimeter ◽  
Setting Time ◽  
Reducing Agent ◽  
Hydration Heat ◽  
Hydration Process ◽  
Early Age ◽  
Cellulose Sulfate

The application of Carboxylmethyl Cellulose Sulfate (CMC-S) in cement paste was studied. The effect of CMC-S on the setting time of cement paste was investigated. Hydration heat of specimens with different cured age was measured via the Hydration Heat Tester (HHT), and hydration process was recorded via Differential Scanning Calorimeter (DSC). The results indicated that CMC-S was a kind of set-retarding and water-reducing agent; its retarding properties appeared at early age, but after three days, the hydration process of cement paste was even improved.

Study on Compatibility of Polycarboxylates Superplasticizer with Different Kinds of Retarders

2012 ◽  
Vol 450-451 ◽  
pp. 543-547
Author(s):  
Gui Bo Gao ◽  
Shi Tao Yan ◽  
Yong Wei Wang ◽  
Chuan Bo Liu
Keyword(s):  
Compressive Strength ◽  
Cement Paste ◽  
Sodium Citrate ◽  
Setting Time ◽  
Small Extent ◽  
Sodium Hexametaphosphate ◽  
Early Age ◽  
Sodium Gluconate ◽  
Influence Mechanism ◽  
Different Ages

In order to study the compatibility between polycarboxyIn order to study the compatibility between polycarboxylates superplasticizer (PC) and different kinds of retarders, sodium citrate (SC), sodium gluconate (SG), sodium hexametaphosphate (SH) and sucrose (SU) were compounded with PC respectively in the same proportion. The liquid degree and its loss of cement paste, the setting time of cement, the blending strength and compressive strength of mortar that admixed with different kinds of retarders were measured, and the influence mechanism of the compatibility between different kinds of retarders and PC were analyzed. The experiment results showed that it was benefit to the liquid degree of cement paste after SG or SH or SU was compounded with PC; The setting time of cement could prolonged more by SH or SU; Blending and compressive strength of mortar in different ages were enhanced in large extent after SG were adopted; The strength of mortar was reduced in early age and enhanced in small extent in mid-later age after SU was compounded. Comprehensively considering to the influence of liquid degree, setting time and strength, the compatibility of SG with PC is higher than other kinds of retarders.

scholarly journals Influence of Nano-SiO2on the Consistency, Setting Time, Early-Age Strength, and Shrinkage of Composite Cement Pastes

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Yu Chen ◽  
Yi-fan Deng ◽  
Meng-qiang Li
Keyword(s):  
Silica Fume ◽  
Cement Paste ◽  
Raw Materials ◽  
Setting Time ◽  
Active Role ◽  
Early Age ◽  
Cement Pastes ◽  
Composite Cement ◽  
Setting Times ◽  
Physical And Chemical

The study outlined the raw materials and mix proportions to prepare composite cement pastes with the addition of silica-based micro- and nanoparticles. The effects of amorphous nano-SiO2on the early-age properties, including the consistency, setting time, early-age strength, and chemical and autogenous shrinkages, were investigated. Under the condition of the same dosage of superplasticizer used, the consistency of cement paste with nano-SiO2is higher than that with silica fume. Significant reductions of the initial and final setting times are observed especially for nano-SiO2addition groups, and the time difference between the initial and final setting times goes up with the increasing proportions of nano-SiO2. The addition of nano-SiO2is more helpful to the improvement of early-age strengths of the paste with or without fly ash admixed than silica fume additive for the same mass proportion. Both the chemical and autogenous shrinkages of cement paste develop with the increasing amount of micro- or nanolevel silica particles; however, nano-SiO2plays a more active role than silica fume in inspiring early-age shrinkage. The physical and chemical mechanisms of nano-SiO2in cement paste are also discussed.

Hydration and Early Age Properties of Cement Pastes Modified with Cellulose Nanofibrils

2020 ◽  
pp. 036119812094599
Author(s):  
Hosain Haddad Kolour ◽  
Warda Ashraf ◽  
Eric N. Landis
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Cement Paste ◽  
Isothermal Calorimetry ◽  
Cellulose Nanofibrils ◽  
Autogenous Shrinkage ◽  
Early Age ◽  
Hydration Reaction ◽  
Cement Pastes ◽  
Degree Of Hydration

In this work, the effects of cellulose nanofibrils (CNFs) on workability, hydration reaction, microstructure, early age shrinkage, fracture properties, flexural strength, and compressive strength of cement paste were investigated. Six batches with variable CNF concentrations with the same water-to-cement (w/c) ratio (0.35) were tested. Flow table test showed a reduction in the workability as CNF dosage increased. Isothermal calorimetry (IC) tests showed that after 3 days, degree of hydration (DOH) improved up to 8% because of the addition of CNFs. Thermogravimetric analysis (TGA) tests at 7 and 28 days showed no significant changes in DOH for all pastes. After 7 days, mixture with 0.15% CNF resulted in up to 31% improvement in compressive strength. For 0.09% CNF addition, cement paste showed 26% increase in compressive strength after 28 days. Tests revealed that adding a small quantity of CNF (0.06%) along with entraining 0.05 extra water reduces autogenous shrinkage by 49% at a cement paste with w/c = 0.30. For interpreting the results, a tunnels, reservoirs, and bridges (TR&B) model is proposed. This model suggests that, as proposed by others, CNFs can modify microstructure by providing tunnels for transporting water to unhydrated cement grain. Because of their hydrophilicity, CNFs retain water and work as reservoirs (internal curing), which explains the improvement in properties at low w/c ratios. Significant increases in fracture energy (up to 60%) and flexural strength (up to 116%) suggest that CNFs are an effective toughening mechanism, acting as bridges that increase the energy required for crack propagation.

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.

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