Moderate Heat Portland Cement Research Articles

The role of metakaolin in pore structure evolution of Portland cement pastes revealed by an impedance approach

Metakaolin has been shown to play a significant role in the pore structure evolution of cementitious materials due to its high pozzolanic reactivity and small fineness. In this work, the early-age evolution of pore structure of moderate heat Portland cement (MHPC) pastes incorporating metakaolin is studied using an innovative impedance approach. Based on the fractal modeling, the pore structure parameters of MHPC blended with metakaolin of various mass percentages up to 20%, including porosity, pore size distribution, pore tortuosity and its fractal dimension, and mean and maximal pore diameters, are determined. The results from the impedance measurements show that the porosity of metakaolin-blended MHPC at both initial hydration and pozzolanic reaction stages increases with the hydration time, which is, respectively, attributed to the dissolution of cement and metakaolin grains. The maximal porosities and the saturation states of MHPC-metakaolin blended pastes occur concurrently due to the dissolution behavior of cement grains. It is concluded that metakaolin incorporation at the 10% replacement ratio is optimal in terms of pore structure refinement of blended cement pastes.

Difference in Strength Development between Cement-Treated Sand and Mortar with Various Cement Types and Curing Temperatures.

To improve the strength of cement-treated sand effectively, the use of various cement types was investigated at different curing temperatures and compared with the results obtained from similar mortars at higher cement contents. The compressive strengths of cement-treated sand specimens that contained high early-strength Portland cement (HPC) cured at elevated and normal temperatures were found to be higher than those of specimens that contained ordinary Portland cement (OPC) and moderate heat Portland cement at both early and later ages. At 3 days, the compressive strength of the HPC-treated sand specimen, normalized with respect to that of the OPC under normal conditions, is nearly twice the corresponding value for the HPC mortar specimens with water-to-cement ratio of 50%. At 28 days, the normalized value for HPC-treated sand is approximately 1.5 times higher than that of mortar, with a value of 50%. This indicates that the use of HPC contributed more to the strength development of the cement-treated sand than to that of the mortar, and the effects of HPC at an early age were higher than those at a later age. These trends were explained by the larger quantity of chemically bound water observed in the specimens that contained HPC, as a result of their greater alite contents and porosities, in cement-treated sand. The findings of this study can be used to ensure the desired strength development of cement-treated soils by considering both the curing temperature and cement type. Furthermore, they suggested a novel method for producing a high internal temperature for promoting the strength development of cement-treated soils.

Environmental evaluation, hydration, pore structure, volume deformation and abrasion resistance of low heat Portland (LHP) cement-based materials

Low heat Portland (LHP) cement is one type of low energy and emission cement. In this work, the abrasion resistance, heat releasing properties, shrinkage behavior and pore structures of LHP cement-based materials are comprehensively investigated, and compared with those of moderate heat Portland (MHP) cement and PC ones. The utilization of LHP cement instead of Portland cement (PC) can effectively reduce the energy consumption (14.1%–15.3%) and CO2 emission (14.9%–15.7%) of concrete. LHP concrete shows the highest final compressive strength among three types of concrete mixtures in this study, which consequently leads to the strongest abrasion resistance. The slow developments of autogenous and drying shrinkage of LHP concrete are exhibited. LHP cement paste possesses better early crack resistance than MHP and PC ones due to its lower shrinkage strain at early age. Besides, the hydration heat of LHP cement paste and adiabatic temperature rise of LHP cement concrete are lower than those of MHP cement and PC ones in all hydration ages. In addition, LHP cement paste has a more refined porous structure than MHP cement and PC ones at late ages, which makes the microstructure of LHP concrete denser and improves the final mechanical properties and abrasion resistance to some degree.

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

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.

Abrasion erosion characteristics of concrete made with moderate heat Portland cement, fly ash and silica fume using sandblasting test

The abrasion erosion characteristics of concrete made from moderate heat Portland cement, fly ash, and silica fume were investigated via sandblasting test. In this study, the influences of fly ash, silica fume, impinging velocity and impinging angle on abrasion erosion resistance were taken into account. The test results indicated that the concrete fabricated with moderate heat Portland cement, fly ash and silica fume was applicable to the mass construction in need of either low hydration heat or high abrasion erosion resistance. The abrasion mass loss rate of concrete increased with the increasing of the impinging angle, and showed an exponential relation with the impinging velocity. Furthermore, the proposed method by Bitter and Neilson et al. was applied to analyze the abrasion erosion characteristics of concrete. The characteristics of each concrete mixture could be featured by four parameters (ε,φ,K, and n) according to this method, and they could be used for preliminarily predicting the abrasion erosion resistance of concrete.

Drying shrinkage and microstructure characteristics of mortar incorporating ground granulated blast furnace slag and shrinkage reducing admixture

This paper presents an experimental study of the effects of cement type, ground granulated blast furnace slag (GGBFS) fineness, curing age, and use of shrinkage reducing admixture (SRA) on the drying shrinkage property and microstructure in mortar. The relationship between drying shrinkage and the microstructure characteristics is determined, and an equation that can reasonably predict the drying shrinkage behavior is also proposed according to the dependent variables. The test results revealed that the drying shrinkage evolution can be significantly affected by the GGBFS powder fineness, the cement type – ordinary Portland cement (N), moderate heat Portland cement (M), and low heat Portland cement (L), and the SRA dosage and pore volume of the mortar, but not the curing age (7 and 28days). For mortar samples without GGBFS, the N and L mortar samples exhibited greater shrinkage strain evolution compared to the M sample. For the case of mortar samples incorporating GGBFS, the L mortar sample exhibited the greatest drying shrinkage strain among the investigated mortar mixes. In addition, the drying shrinkage increased significantly with the increase in the GGBFS fineness for the M and L Portland cement mortars. Moreover, the addition of SRA could effectively reduce the drying shrinkage, which is mainly controlled by the pore size distribution and mass loss. In the case of mortar without and with SRA, the drying shrinkage was found to have a high correlation with the pore size ranges of 6–30nm and 0–20nm in diameter, respectively. As a result of the high correlation of pore volume and mass loss observed in this study, the prediction equation for the drying shrinkage of GGBFS mortar is proposed, which verifies good accuracy compared to the test results.

Seawater Corrosion Resistance of Low Heat Portland Cement Concrete

With the analysis of the seawater corrosion effect on low-heat Portland cement concrete under wetting-drying test, the compressive strength and quality change of concrete test specimen were investigated for different test periods. According to the evaluation of seawater corrosion resistance, the low-heat Portland cement showed better corrosion resistance than that of ordinary Portland cement and moderate-heat Portland cement. Moreover, the corrosion mechanism was expounded through XRD and SEM analysis. It was found that lots of C2S in the low-heat Portland cement play an important role in corrosion resistance of cement concrete.

Experimental Study on Compatibility between Alkali-Free Liquid Concrete Accelerators and Cement

This paper selected two kinds of alkali-free liquid concrete accelerators and tested their compatibility with ordinary Portland cement, Portland cement and moderate heat Portland cement by measuring the setting times, compressive strength and compressive strength ratio of samples. The results showed that the compatibility is good between alkali-free accelerators and two types of cement: ordinary Portland cement and moderate heat Portland cement. However, the compatibility of two accelerators and Portland cement are quite different, the compatibility of AFA-2 accelerator is excellent, but AFA-1 accelerator is very poor. The setting times of alkali-free accelerators is mainly influenced by the mixing materials content, gypsum content, C3A and C3S content. In order to ensure the mechanical properties and durability of concrete, the setting times of new concrete accelerator is not the shorter the better, the appropriate initial and final setting times are 1min30s~5min and 4min~ 12min respectively.

Production Quality Control of Moderate Heat Portland Cement and Analysis of Application Effect in Roller Compacted Concrete

Moderate Heat Portland Cement is not only frequently-used cement for dam but also one of the largest amount of special cement as a main cementitious materials of concrete in hydraulic structure in China. Due to the high quality requirement and the complicated technology in the construction of dam, a series of measures are adopted to control the production quality of Moderate Heat Portland Cement used in the dam construction. In this paper, the measures of production quality control of the Moderate Heat Portland Cement are introduced, including controlling the raw materials such as the cement raw meal, fuel, clinker and gypsum, managing the discharge from the mill and the entrance test, which ensure that the various targets of physical and mechanical indexes are in accordance with the standard requirement. Moreover, the engineering quality of Roller Compacted Concrete (RCC) for the dam is effectively guaranteed through the lower pot temperature and the less hydration heat. The construction experience is available for the like-kind engineering interiorly.

Performances of Belite-Rich Cement Concrete with Fly Ash and Phosphorous Slag Powder

This paper presents the results of laboratory and outdoor exposure site studies on belite-rich cement concrete with phosphorous slag powder and fly ash. The parameters studied included strength, hydration heat, ultimate elongation, Young’s modulus, and adiabatic in temperature. The experimental results showed that belite-rich cement resulted in a higher rate of strength development of mortar and concrete at later ages when compared with that of moderate-heat Portland cement. And the hydration heat of belite-rich cement is lower than that of reference. This is due to the different phase composition of the two cements. Belite-rich cement contains less C3S but more C2S than moderate-heat Portland cement. In addition, belite-rich cement concrete with phosphorous slag powder and fly ash exhibited better performances than those of moderate-heat Portland cement concrete.

DRYING SHRINKAGE OF HARDENED CEMENT PASTE UNDER DIFFERENT TEMPERATURE

Length-change isotherm and desorption isotherm of hardened cement pastes whose water to cement ratio is 0.55 and cements used are ordinary portland cement, moderate heat portland cement, and low heat portland cement were measured in 20°C and 40°C degrees Celsius. In addition, vapor adsorption isotherm for BET surface area, Young's modulus and Poisson's ratio for bulk modulus under compressive loading test, and density of hardened cement paste and water content were measured. As a result, the higher temperature showed smaller water content and smaller shrinkage under desorption process. This phenomenon can be explained by the hydrophobic properties of the surface of the hardened cement paste in the higher temperature condition or the temperature and relative humidity dependency of surface area of hardened cement paste. Both hypothesis are reasonable and consistent with existing reports.

PREDICTION METHOD OF COMPRESSIVE STRENGTH OF CONCRETE USING EQUIVALENT AGE

The aim of this research is to propose a method to predict the strength development of concrete using equivalent age. The experiment of strength development was carried out. Ordinary Portland cement, moderate-heat Portland cement and low-heat Portland cement were used for concrete specimen. Water cement ratio was ranged from 0.3 to 0.6. Strength development of concrete cured below subzero temperature was examined too. The result showed that the apparent activation energy in equivalent age equation depends on mineral composition of cement. Furthermore, the effect of freezing on the reaction rate of strength development was shown. Consequently, the strength development of concrete can be estimated from mineral composition of cement, nominal strength of concrete and curing temperature by the method proposed in this paper.

Multi-powder dam concrete with high performance and low adiabatic temperature rise

Based on the fluidity, strength, heat of hydration and loop crack resistance experiment of multi-powder paste, the components and proportion of multi-powder were optimized and the concrete properties were studied. The multi-powder consists of limestone powder, slag, fly ash and moderate heat Portland cement (PMH cement). The results show that the compressive strength of the multi-powder paste and mortar is close to those of PMH cement, fly ash paste and mortar currently used in dam concrete, yet the flexural strength is relatively higher. The multi-powder paste is featured by larger fluidity, lower heat of hydration and delayed cracking time. In comparison, less unit water consumption and cement is used in multi-powder concrete, and under premise of equal mechanical performance, deformation, thermal performance and durability, the adiabatic temperature rise at 28 d is reduced by 2 °C. In this way, the crack resistance is improved and it is feasible both technically and economically to produce HPC for dam concrete.

BASIC STUDY ON TEST AGE AND CURING METHOD OF SPECIMEN FOR MANUFACTURING CONTROL OF HIGH STRENGTH CONCRETE

Test age and curing method of specimen for manufacturing control of high strength concrete were investigated and following results were obtained. 1) The strength correction value of high strength concrete is small in the order of Ordinary portland cement > Moderate heat portland cement > Low heat portland cement. Moreover, it was necessary to set test age of high strength concrete using Moderate heat portland cement and Low heat portland cement on the day after the 28th. 2) In the case to use portland cement, if strength test is set within 91 days, the strength correction value doesn't reach a big negative value. 3) In the case of binder water ratio is six to seven, even if strength test is set within 91 days, the strength correction value reaches a big negative value. 4) Also in the case with 3), reasonable manufacturing control can be done by the hot water cured specimen.

STRENGTH DEVELOPMENT OF CONCRETE AND STRENGTH CORRECTION VALUE OF CONCRETE USING VARIOUS CEMENTS IN STRUCTURE

The strength development of concrete using various cement, i.e. ordinary portland cement, moderate heat portland cement, blast furnace slag cement type B etc. in structure are investigated based on the data of some experiments carried out in past time. The purpose of this paper is to consider relationship strength development of core specimen from 28days to 91days and mean temperature, and to establish the strength correction value of concrete. The following results were obtained; The strength development from 28days to 91days of core specimen was about 5-10N/mm2 ranges regardless of kinds of cement. The compressive strength of core specimen at 91days was expressed by function of strength of core specimen at 28days and mean temperature. The strength correction value of concrete was suggested.

EFFECTS OF TIME INTERVAL FOR PLACING ON CONSOLIDATED FRESH CONCRETE AND THE BONDING STRENGTH WITH VARIOUS CEMENTS

Recently, increasing various constructions, we can choose various cement for each concrete constructions, suited their performance. We studied properties and time interval for placing on consolidated fresh concrete with fresh concrete with ordinary portland cement, moderate-heat portland cement, portland blast-furnace slag cement, portland fly ash-cement, and eco-cement. And we prepared influence of the durability of placing joint. The results suggested, ordinary portland cement had high compressive strength and eco-cement had less bleeding water. Additionally, the results showed the time interval of placing influenced the termination time of bleeding with various cements.

Anti-crack performance of low-heat Portland cement concrete

The properties of low-heat Portland cement concrete (LHC) were studied in detail. The experimental results show that the LHC concrete has characteristics of a higher physical mechanical behavior, deformation and durability. Compared with moderate-heat Portland cement (MHC), the average hydration heat of LHC concrete is reduced by about 17.5%. Under same mixing proportion, the adiabatic temperature rise of LHC concrete was reduced by 2℃-3℃,and the limits tension of LHC concrete was increased by 10×10^(-6)-l5×10^(-6) than that of MHC. Moreover, it is indicated that LHC concrete has a better anti-crack behavior than MHC concrete.

Long-term performance of moderate heat Portland cement with double-expansive sources

The long-term performance of moderate heat Portland cement with double-expansive sources (DE cement) in the system of high MgO clinker and gypsum was studied by XRD, SEM/EDAX and test methods for strength and expansion of cement. Results indicate that the periclase particle, whose size was 5–7.5 μm in DE cement clinker containing 4.8 % MgO, existed individually. The periclase hydration in hardened DE cement paste started at about 60 days and completed up to 2 000 days, and ettringite in the paste was stable from 3 days to 2 000 days. Under the conditions of 4.5%–5.0 % MgO in clinker and 2.8%–3.4 %SO3 in cement, ettringite expansion and brucite expansion in DE cement paste had a continuity, entirety and stability. At the ages of 90, 365, 730 and 2 000 days the expansion of the paste reached 0.07%–0.11%, 0.16%–0.21%, 0.21%–0.27 % and 0.29%–0.38 %, respectively. The results suggest that by using this cement in mass concrete it may compensate its temperature shrinkage and autogenous shrinkage to some extent.

３０年間常時海水中に暴露されたコンクリートの諸性質について

A detailed investigation on 30-years old concrete specimens of 150 mm in diameter and 300 mm in height made with ordinary portland cement (OPC), high early strength portland cement (HES), moderate heat portland cement (MH), slag cement of type B (SCB), and alumina cement (AL) was carried out. In each specimen, steel bars were embedded at cover depths of 20, 40, and 70 mm. Mineralogy and microstructure of mortar portions at the inner and outer regions, coarse aggregate-mortar interface and steel-concrete interface were investigated. Carbonation depth, acid-soluble chloride contents, electro-chemical and corrosion condition of embedded steel bars were evaluated. It is concluded from the results that the microstructure of concrete at the outer region for SCB and AL becomes denser compared to the inner region. For AL, the inner region is relatively more porous and also a porous steel-concrete interface is found. Chloride ingress in concrete was lower for SCB and AL compared to OPC, HES and MH. However, more corrosion over the steel bars was found for AL. The surface condition of the steel bars embedded in concrete made with SCB remains as same as the initially polished condition. Utilization of SCB is concluded as one of the best choices to improve long-term durability of marine concrete structures.

中庸熱ポルトランドセメントを用いた高強度コンクリートの諸性状および構造体強度と水セメント比の関係

Moderate-heat portland cement has likely been applied to mass concrete where as in this study it is applied to high-strength concrete with a designed strength ranging from 36 to 70 N/mm2. Fresh properties, strength development and temperature histories of full-scale model specimens of the high-strength concrete have been investigated. It was found that high-strength concrete with moderate-heat cement can be fully applicable to real construction practice on site. Moreover, some important prediction formulas and parameter value were derived : the maximum temperature of the model specimen with parameters of unit cement content and concrete temperatures, relationship between core strength and simplified adiabatic temperatures and a water-cement ratio by which column strengths in structure can satisfy the designed strength.