Carbonation of Pure Minerals in Portland Cement:Evolution in Products as a Function of Water-to-solid Ratio

Minerals in Portland cement including tricalcium silicate(C_(3)S),β-dicalcium silicate(β-C_(2)S),tricalcium aluminate(C_(3)A),and tetracalcium ferroaluminate(C_(4)AF),show a significantly different activity and product evolution for CO_(2)curing at various water-to-solid ratios.These pure minerals were synthesized and subject to CO_(2)curing in this study to make an in-depth understanding for the carbonation properties of cement-based materials.Results showed that the optimum water-to-solid ratios of C_(3)S,β-C_(2)S,C_(3)A and C_(4)AF were 0.25,0.15,0.30 and 0.40 for carbonation,corresponding to 2 h carbonation degree of 38.5%,38.5%,24.2%,and 21.9%,respectively.The produced calcite duringβ-C_(2)S carbonation decreased as the water-to-solid ratio increased,with an increase in content of metastable CaCO_(3)of vaterite and aragonite.The thermodynamic stability of CaCO_(3)produced during carbonation was C_(3)A>C_(4)AF>β-C_(2)S>C_(3)S.The carbonation degree of Portland cement was predicted based on the results of pure minerals and the composition of cement,and the error of predicted production of CaCO_(3)was only 1.1%,which provides a potential method to predict carbonation properties of systems with a complex mineral composition.

Effect of Hydrated Calcium Aluminate Cement on the Chloride Immobilization of Portland Cement Paste

To improve the efficiency and stability of chloride immobilization of portland cement paste,hydrated calcium aluminate cement(HCAC)prepared by wet grinding of CAC was added into portland cement paste as an additive.The immobilized chloride ratio(ICR)was evaluated,and the mechanism of chloride immobilization was researched by XRD,DTG,NMR,and MIP tests.The analysis results demonstrated that HCAC could improve the chloride immobilization capacity of portland cement paste.The mechanism was attributed to the following aspects:chemical binding capacity was enhanced via producing more Kuzel’s salt;physical adsorption capacity was reduced by decreasing the C-S-H gel;migration resistance was enhanced through refining the pore structure.

Research Progress of Eco-Friendly Portland Cement Porous Concrete:A Review

With the great impetus of energy conservation and emission reduction policies in various countries,the proposal of concepts such as“Sponge City”and“Eco-City”,and the emphasis on restoration and governance of ecological environment day by day,portland cement porous concrete(PCPC),as a novel building material,has attracted more and more attention from scientific researchers and engineers.PCPC possesses the peculiar pore structure,which owns numerous functions like river embankment protection,vegetation greening as well as air-cleaning,and has been of wide application in different engineering fields.This paper reviews the salient properties of PCPC,detailedly expounds the research progress of domestic and foreign literature about this subject in the past ten years(2010–2020),conducts the statistical analysis of the distribution rule of its major properties around the world,combines with the engineering application to summarize the excellent properties of PCPC,and makes a forecast of future research direction.

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^-6-15×10^-6 than that of MHC. Moreover, it is indicated that LHC concrete has a better anti-crack behavior than MHC concrete.

Properties of Belite-Rich Portland Cement and Concrete in China

Performances of belite-rich Portland cement, or HBC （high belite cement）, and the resultant concrete are introduced by comparing with that of alite based PC （Portland cement） and concrete. The comparison study of cement properties indicates that HBC possesses the properties of less water demand for normal consistency, better compatibility with water reducer, higher later age strength after 28-day under standard curing temperature of 20 ℃, unique strength gain under elevated curing temperatures of 38-70 ℃, lower hydration heat evolution and temperature rise, lower drying shrinkage and excellent resistance to sulphate attack. These results have been demonstrated by the comparison performance evaluation of concretes prepared by HBC and PC in terms of workability, physical mechanical properties and durability when making high performance high strength concrete and massive concrete.

INVESTIGATIONS ON THE INTERFACIAL ZONE BETWEEN AGGREGATE AND PASTE OF PORTLAND CEMENT

The composition and structure of the inter facial zone between aggregate and paste of Portland cement as well as the orientation coefficient of portlandite ( Icn ) were preliminarily studied by XRD and SEM methods. The main products in the zone are C -S-H gel, portlandite, AFt and pores, micro-cracks as welt as unhydrated portland cement clinker particles. Potlandite not only grows well but exists in orientating forms, and near the interface it exists in a state parallel to the surface of aggregate by its (001) lattice plane. Icn rises with the increase of cement water ratio (w/c) and the development of the cement hydration. The higher the w/c, the more the pores and micro-cracks in the zone. w/c bears an exact relation to the decrease of bond strength. Icn, is decreased when 5. 0% silica fume is added to cement. Bond strengths at early ages are reduced by adding 0. 5% FDN (one kind of water-reducing admixture) due to the retarded hydration of cement, but they will increase continually and become greater than those of other samples after 28 days.

危重患者应用Portland方案强化胰岛素治疗的护理策略

危重患者血糖升高不仅和疾病的严重程度相关,同时也是影响预后的重要因素之一。胰岛素强化治疗可以控制危重患者的目标血糖控制（Target Glucose Control，TGC）在4．4～6．1mmol／L之间，从而大大降低相关的临床并发症和病死率。

Portland cement修复磨牙髓室底穿孔的实验研究

目的评估波特兰水门汀(Portland cement,PC)直接修复磨牙髓室底穿孔的效果,并与无机三氧化聚合物(mineral trioxide aggregate,MTA)作比较。方法选取人新鲜拔除的恒磨牙53颗,按随机数字表法分为PC、MTA2个实验组(n=24)和1个对照组(n=5)。实验组在髓室底中央制备直径2 mm的穿孔模型,分别用PC和MTA修复穿孔。对照组只开髓不制备穿孔模型。利用体视显微镜观察修复后样本的根分叉形态。扫描电子显微镜(SEM)观察材料和牙体组织的结合界面,并测量结合界面间隙宽度。采用葡萄糖定量法分析模型检测微渗漏值。结果体视显微镜下两实验组对根分叉外形修复均达到了良好效果。SEM观察显示PC和MTA与牙体组织之间均可见不连续的微间隙存在,PC与牙体组织间隙宽度为(7.363±2.159)μm,MTA与牙体组织间隙宽度为(8.693±3.551)μm,两者无明显差异(P>0.05)。在观察期内,虽然PC组的微渗漏值小于MTA组,但无统计学差异(P>0.05)。结论 PC与MTA修复髓室底穿孔的封闭效果相当,且PC价格低廉,不易使牙体变色,可以考虑作为MTA替代材料进一步研究。

明胶掺杂对Portland水泥理化性质的影响

无机三氧化物聚合物是一种被广泛使用的牙根管充填材料。作为其主要成分的Portland水泥一直被研究在牙齿修复材料领域作为无机三氧化物聚合物的替代物。在本论文研究工作中,我们制备了明胶/Portland水泥复合材料,研究了明胶添加量对Portland水泥理化性质的影响。不同量的明胶被添加到Portland水泥中,通过水化硬化过程,获得明胶掺杂的Portland水泥水化硬化体。测定了不同明胶掺杂量下,标准水泥稠度的用水量;在标准水泥稠度下,研究了明胶掺杂对Portland水泥凝固时间以及安定性的影响。考察了明胶掺杂对Portland水泥3天抗压强度和抗折强度的影响。结果表明明胶的掺杂显著延长了Portland水泥的凝固时间,但对标准水泥稠度用水量、安定性等性质没有显著影响。明胶的掺杂使得Portland水泥的3天抗压强度和抗折强度有所降低。

Portland Cement用于根尖屏障材料的封闭性研究

目的通过离体实验观察波特兰水门汀(Portland Cement,PC)作为根尖屏障的封闭性,并将其与无机三氧化物聚合物(mineral trioxide aggregate,MTA)、玻璃离子水门汀(glass ionomer cement,GIC)、银汞合金(amalgam,Am)作比较。方法选取单根前磨牙64颗,行根管预备并制备根尖开放模型。完全随机分组法将实验用离体牙分为A、B、C、D 4个实验组,根尖部分别充以PC、MTA、GIC、Am,每组15个样本,阴性对照组及阳性对照组每组各2个样本。使用4%牛血清白蛋白作为观测指标连续观测60 d,用考马斯亮蓝染色技术对蛋白渗出做定量测定。结果 A组与B组蛋白渗出量无明显统计学差异,A组与C、D组蛋白渗出量比较有统计学差异(P<0.05),B组与C、D组蛋白渗出量比较有统计学差异(P<0.05)。随着时间的延长,A组蛋白渗出量的增加无统计学意义。结论 PC的根尖封闭性与MTA相当,且明显优于GIC、Am。

Properties of high calcium fly ash geopolymer pastes with Portland cement as an additive

The effect of Portland cement （OPC） addition on the properties of high calcium fly ash geopolymer pastes was investigated in the paper. OPC partially replaced fly ash （FA） at the dosages of 0, 5%, 10%, and 15% by mass of binder. Sodium silicate （Na2SiO3） and sodium hydroxide （NaOH） solutions were used as the liquid portion in the mixture： NaOH 10 mol/L, Na2SiO3/NaOH with a mass ratio of 2.0, and alkaline liquid/binder （L/B） with a mass ratio of 0.6. The curing at 60℃ for 24 h was used to accelerate the geopolymerization. The setting time of all fresh pastes, porosity, and compressive strength of the pastes at the stages of 1, 7, 28, and 90 d were tested. The elastic modulus and strain capacity of the pastes at the stage of 7 d were determined. It is revealed that the use of OPC as an additive to replace part of FA results-in the decreases in the setting time, porosity, and strain capacity of the paste specimens, while the compressive strength and elastic modulus seem to increase.

Effect of Fine Steel Slag Powder on the Early Hydration Process of Portland Cement

Hydration heat evolution, non-evaporative water, setting time and SEM tests were peorormed to investigate the effect of fine steel slag powder on the hydration process of Portland cement and its mechanism. The results show that the effect of fine steel slag powder on the hydration process of Portland cement is closely related to its chemical composition, mineral phases, fineness, etc. Fine steel slag powder retards the hydration of portland cement at early age. The major reason for this phenomenon is the relative high content of MgO , MnO2, P2O5 in steel slag, and MgO solid solved in C3 S contained in steel slag.

The Durability of Alkali-Activated Materials in Comparison with Ordinary Portland Cements and Concretes:A Review

China is the largest producer and user of ordinary Portland cement(OPC),and the rapid growth of infrastructure development demands more sustainable building materials for concrete structures.Alkali-activated materials(AAMs)are a new type of energy-saving and environmentally friendly building material with a wide range of potential applications.This paper compares the durability of AAMs and 0 PC-based materials un der sulfate attack,acid corrosion,carb on ation,and chloride penetratio n.Different AAMs have shown distinct durability properties due to different compositions being formed when different raw materials are used.According to the calcium(Ca)concentration of the raw materials,this paper interprets the deterioration mechanisms of three categories of AAMs:calcium-free,low-calcium,and calcium-rich.Conflicts found in the most recent research are highlighted,as they raise concerns regarding the consistenee and long-term properties of AAMs.Nevertheless,AAMs show better durability performances than OPC-based materials in general.

Serviceability and Reinforcement of Low Content Whisker in Portland Cement

In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanical properties of portland cement were investigated. The experimental results show that CaCO3 whiskers have a good stability and serviceability in cement, and should not significantly alter the rheological properties of the cement paste. The flexural and compressive strength of portland cement reinforced by CaCO3 whiskers was increased by 33.3% and 12.83%, respectively.

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.

Morphology Difference between the Alkali Activated Cement and Portland Cement Paste on Multi-scale

The features of alkali activated slag（AAS） and portland cement （PC） were observed on multi-scale,the crack and fracture sections were observed with naked eyes,and SEM and AFM were used to study the structure morphology differences between PC and AAS on micrometer to nano meter scale.The experimental results indicated that the AAS paste had soil like fracture texture and it was composed of mainly C-S-H gel but lacks of crystals,and it had a very strong tendency to shrink and crack.AAS paste is much denser and more homogeneous than PC,and on the nano scale C-S-H nano particle in the AAS paste is much smaller and packs much denser than PC paste.

Effect of Calcium Aluminate Cement Variety on the Hydration of Portland Cement in Blended System

Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.

Influence of Cellulose Ethers on Hydration Products of Portland Cement

Cellulose ethers are widely used to mortar formulations,and it is significant to understand the interaction between cellulose ethers and cement pastes.FT-IR spectra,thermal analysis and SEM are used to investigate hydration products in the cement pastes modified by HEMC and HPMC in this article.The results show that the hydration products in modified cement pastes were finally identical with those in the unmodified cement paste,but the major hydration products,such as CH（calcium hydroxide）,ettringite and C-S-H,appeared later in the modified cement pastes than in the unmodified cement paste.The cellulose ethers decrease the outer products and increase inner products of C-S-H gels.Compared to unmodified cement pastes,no new products are found in the modified cement pastes in the present experiment.The HEMC and HPMC investigation shows almost the same influence on the hydration products of Portland cement.

Spectrophotometric Determination of Water-Soluble Hexavalent Chromium and Determination of Total Hexavalent Chromium Content of Portland Cement in the Presence of Iron (III) and Titanium (IV) Using Derivative Ratio Spectrophotometry

A rapid, reliable and accurate method for the determination of hexavalent chromium in Portland cement is developed. The proposed method includes direct spectrophotometric determination of Cr (VI) in Portland cement with 1, 2, 5, 8 Tetrahydroxyanthraquinone, (Quinalizarin, QINZ) at pH 1.5. The European Directive (2003/53/EC) limits the use of cements so that it contains no more than 2 mg.Kg-1 of water-soluble Cr (VI). The absorbance at 565 nm due to Cr (VI)-QINZ complex is recommended for the determination of water-soluble Cr (VI) in Portland cement. The quantification of Cr (VI) released from cement when mixed with water is performed according to TRGS 613 (Technical Rules of Hazardous Substances). The validity of the method is thoroughly examined and the proposed method gives satisfactory results. A derivative spectrophotometric method has been developed for the determination of total Cr (VI) in Portland cement in the presence of Fe (III) and Ti (IV). The hexavalent chromium complex formed at pH 1.5 allows precise and accurate determination of chromium (VI) over the concentration range 0.05 to 3.0 mg.L-1of chromium (VI). The validity of the method was examined by analyzing several Standard Reference Material (SRM) Portland cement samples. The MDL (at 95% confidence level) was found to be 25 ng/mL for chromium (VI) in National Institute of Standards and Technology (NIST) cement samples using the proposed method.

Influence of Benzenediols—Pyrocatechol and Resorcinol—On the Resistance of Portland Cement Mortars with Aluminum Sulfate to Sulfate Attack

The effect of benzene-1,2-diol (pyrocatechol) and benzene-1,3-diol (resorcinol) on the development of sulfate attack in Portland cement mortars containing alkali-free setting accelerator (aluminum sulfate) was studied. It has been found that these compounds (especially pyrocatechol—due to its ability to form chelate complexes with aluminum ions) restrain destructive deformations of Portland cement mortars with aluminum sulfate admixture when under test conditions a constant supply of sulfate ions from external source is provided. According to 27Al-MAS NMR data, pyrocatechol does not influence the amount of ettringite formed in Portland cement paste during its store in sodium sulfate solution. Presumably, in presence of benzenediols, in cement mortars with aluminum sulfate admixture the formation of ettringite crystals with a less pronounced destructive effect takes place.