长侧链两性聚羧酸系减水剂对水泥早期水化的影响

考察了不同阳离子含量的长侧链两性聚羧酸系减水剂(APCs)对水泥早期水化的影响。结果表明,相较于纯阴离子型的普通聚羧酸系减水剂PCs,含阳离子的APCs能够加速水泥的水化,促进早期水化产物生成,从而提高水泥早期强度。当共聚物中阳离子的含量为10%时(APC-10),水泥浆体最快进入水化加速反应阶段。热重与扫描电镜的结果也证实,在相同的龄期内,掺APC-10的样品中生成更多的羟钙石和簇状水化产物。但随着阳离子含量的进一步增加,长侧链两性聚羧酸减水剂对水化的促进作用减弱甚至消失,试件的早期强度反而有所降低。     

掺梳形减水剂水泥浆体早期水化产物形貌研究

为揭示梳形减水剂对水泥早期水化的影响规律,指导工程应用,通过SEM分析,研究了掺用3种典型结构的梳形减水剂的水泥浆体早期水化产物形貌及其电子特征数据。结果表明,梳形减水剂加速了水泥早期水化反应,且丙烯酸类、马来酸类共聚物分别促进了AFt、AFm的形成。因此,梳形减水剂品种对水泥早期水化和混凝土工程性能具有较大影响,应根据使用要求合理选用,必要时与缓凝剂、引气剂或消泡剂复合使用。     

梳型长短侧链聚羧酸减水剂对水泥早期水化行为的影响及作用机理EI北大核心CSCD

调节异戊烯醇聚氧乙烯醚(TPEG)的聚合度及与丙烯酸(AA)的摩尔比,以过硫酸铵(APS)为引发剂、甲基丙烯磺酸钠(MAS)为链转移剂,通过水溶液自由聚合法合成了长侧链聚羧酸(LPCE)、长短侧链聚羧酸(LSPCEs)和短侧链聚羧酸(SPCE)3类梳型聚羧酸减水剂(PCEs)。研究了长短侧链比例对水泥早期水化行为的影响,进一步通过PCEs水溶液聚集形态、吸附性能和引气性能等探讨了长短侧链比例对水泥水化行为影响的作用机理。结果表明,SPCE有利于延缓水泥的早期水化,使水化诱导期延长,这是由于SPCE较LSPCEs和LPCE,在水泥颗粒表面的吸附量更大、吸附层厚度更高所致。加入水泥后,随着短侧链比例的增大,PCEs水溶液的起泡高度有增加趋势,而LPCE水溶液的黏度较大,稳泡性能较LSPCEs和SPCE好。     

C-S-H纳米晶种及其对水泥水化硬化的促进作用综述

近些年来的研究发现，将一些纳米粒子加入到水泥中，可以为水化产物提供更多形核位点，降低水化产物的形核势垒，加快水泥的水化进程。这些纳米材料包括纳米SiO₂、纳米CaCO₃、纳米TiO₂、碳纳米管、纳米水化硅酸钙(C-S-H)等。其中，人工合成的纳米C-S-H晶种与水泥水化产物C-S-H凝胶具有相似的化学组成，是C-S-H凝胶的良好的形核基质，在众多晶种材料中，对水泥水化的加速作用最为显著，成为近年来的研究热点。到目前为止，众多学者围绕C-S-H微/纳米材料的成核方式、制备方法及对水泥水化的促进机理进行了大量研究，发现采用共沉淀法在聚合物存在的条件下制备的纳米C-S-H晶种成核剂遵循非经典成核方式，其具有纳米级的晶粒尺寸和良好的分散稳定性。将纳米C-S-H晶种以一定掺量加入到水泥中，可以充当水泥水化产物C-S-H凝胶的额外成核位点，极大地降低了C-S-H凝胶的成核势垒，有效地促进了水泥水化速率和早期强度的发展，尤其可以显著提升水泥1 d龄期以内的强度。与常用的早强剂相比，这种纳米C-S-H晶种成核剂除具有掺量低、早强效果好、...     

复合外加剂对铬铁渣基复合材料水化机理的影响

采用X射线粉末衍射(XRD)、差热-热重同步热分析仪(TG-DSC)、扫描电子显微镜(SEM)等分析铬铁渣基复合材料的水化产物的物相组成、微观结构和形貌特征,用甲醇法测定了复合材料的孔隙率。研究了复合外加剂对复合材料水化性能的影响及其作用机理。研究表明:掺入外加剂能显著提高复合材料的早期强度,水化初期大量的钙矾石(AFt)和水化硅酸钙凝胶(C-SH)是复合材料早期强度的主要来源,水化后期外加剂能促进铬铁渣、矿渣等的二次水化反应,使其水化速度增长较快。C-S-H凝胶的不断形成和增多及其对体系孔隙的填充使复合材料的结构更加致密。     

硫铝酸盐复合水泥体系水化特征研究

通过正交试验研究了硫铝酸盐复合水泥中不同掺量的普通硅酸盐水泥、石膏、硅灰及粉煤灰对其强度、自收缩以及水化热的影响。结果表明:普通硅酸盐水泥及石膏的掺入显著改变了硫铝酸盐复合水泥水化进程,硅灰及粉煤灰是影响后期强度的主要因素;自收缩试验结果表明普通硅酸盐水泥和石膏是影响硫铝酸盐复合水泥水化早期自收缩的主要因素;水化热测试结果表明粉煤灰和普通硅酸盐水泥在水化前6 h起到显著作用,粉煤灰降低了水化放热,而普通硅酸盐水泥增加水化放热;硅灰及石膏对6~24 h水化放热影响显著。结合XRD及SEM测试结果,表明普通硅酸盐水泥和石膏的存在加速了硫铝酸盐复合水泥水化早期钙矾石生成,随着石膏浓度的下降,发生转晶(AFm),随着后期硫铝酸盐水泥中β-C₂S的水化以及硅灰、粉煤灰的火山灰反应产生C-S-H凝胶,使得体系致密化。     

利用红外和核磁技术分析矿渣硅酸盐复合胶凝材料的水化产物

采用傅里叶红外光谱(FTIR)和高分辨29Si固体核磁共振技术(NMR),研究了不同水化龄期的水泥-矿渣复合胶凝硬化浆体的微观结构。结果表明:纯硅酸盐水泥随着水化时间的增长,水化程度变大,聚合度增加,生成更多的长链水化硅酸钙(C-S-H)凝胶;矿渣硅酸盐水泥试样水化早期主要生成二聚体凝胶,随着龄期增长,逐渐转变为长链型凝胶,平均链长逐渐增加;随着矿渣掺量的增加,激发矿渣所需时间增长,早期Q~2(1Al)很少,但随着龄期延长,矿渣逐渐被激发,C-A-S-H凝胶变多。     

磨细石灰石粉对减水剂-水泥适应性的影响

采用化学分析、热分析、Zeta电位分析等手段研究聚羧酸和萘系减水剂在磨细石灰石粉存在下与水泥的适应性。结果表明:在磨细石灰石粉存在下,聚羧酸减水剂促进水泥水化初期钙矾石和单碳型水化硫铝酸钙的生成,降低水泥对减水剂的吸附;而萘系减水剂的吸附量大,石灰石粉加速了水泥颗粒表面的减水剂被生成的水化产物覆盖的过程,导致流动度损失加快。因此,在石灰石粉存在下,聚羧酸减水剂的适应性较萘系减水剂更佳。     

甲酸钙对硫铝酸盐水泥早期水化过程的影响

利用维卡仪、水化放热速率、XRD、TG-DSC和SEM等测试手段,研究了甲酸钙(Ca(HCOO)2)对硫铝酸盐水泥凝结时间、水化历程和水化产物及微观形貌的影响。结果表明,Ca(HCOO)2可明显促进硫铝酸盐水泥的凝结,并缩短初凝和终凝时间间隔;显著缩短了硫铝酸盐水泥的水化诱导期,且使水化加速期提前,使第一水化热峰值提高32%,但对水化稳定期的水化放热速率无明显影响;Ca(HCOO)2可以提高硫铝酸盐水泥水化环境的碱度,在早期提高了水化产物钙矾石(AFt)的结晶度,水化早期生成的水化产物结构致密,但并不改变水化稳定期的水化产物和微观形貌。     

水泥水化产物——水化硅酸钙(C-S-H)的研究进展

水化硅酸钙(C-S-H)作为水泥基材料的主要水化产物,决定着水泥基材料的强度发展、收缩、徐变和结构的服役寿命,被称为水泥基材料的"基因".对C-S-H组成、结构和性能的充分认识有助于理解水泥基材料微结构的形成机理,进而对其性能进行自下而上的设计和调控.近年来先进测试和分析技术的发展为C-S-H基本性能的研究提供了新思路.C-S-H的成核生长理论、力学性能提升以及形貌调控等逐渐成为当前研究热点,已取得重要进展.学者们大多采用合成的方法制备体系纯净且具有一定结晶度的C-S-H,并以此研究水泥体系中无定形C-S-H凝胶的基本性能.研究发现,双分解合成C-S-H的成核生长过程中存在球形中间体,其最终转化为箔片状形貌的产物,遵循非经典的成核生长方式.在亚粒子尺度,越来越多的结构信息表明,与尖乃石相比,C-S-H的结构与托贝莫来石更为接近;在粒子尺度上,CM凝胶系列模型被广泛应用于解释C-S-H比表面积等物理参数以及水泥基材料收缩徐变的机理.C-S-H的Ca/Si、含水量、硅链聚合程度以及形貌等微纳结构的广泛研究为建立C-S-H微纳结构与宏观性能之间的联系提供了丰富的数据支撑.对C-S-H进行本征结构调控有望从根本上改善水泥基材料韧性差的力学特征,许多学者试图从孔结构调控、有机和无机复合材料构建以及纳米材料改性等方面提升C-S-H的力学性能,取得了一定突破.本文系统总结了C-S-H的合成方法、成核生长理论、结构模型;主要从Ca/Si、含水量、硅链聚合程度以及形貌四个方面综述了C-S-H的微纳结构;围绕形貌和力学性能介绍了C-S-H的调控和设计方法;分析了目前存在的研究不足并提出了未来的发展方向,以期为全面认识C-S-H以及水泥基材料的性能调控提供借鉴.     

Influence of dispersing agents on the rheology and early heat of hydration of blended cements with high loading of calcined marl

The dispersing effectiveness of five commercial plasticizers; lignosulfonate (LS), naphthalene sulphonate–formaldehyde polycondensate (NSF) and three polycarboxylate ethers (PCEs) were quantitatively investigated in blended cements where ordinary Portland cement (OPC) was partly replaced by calcined marl (CM) up to 60%. CM drastically viscosified and decreased the flow of the cement due to high absorption of water. The performance of plasticizers mimics that in the OPC system except when PCEs were added. PCEs possessing long side chains were less effective as dispersants due to the consumption of these polymers via the ability of their PEO side chains to intercalate between the remaining layers in the calcined clay. Higher dosages were thus needed for effective dispersion. The decrease in PCE–OPC interaction led to little retardation in cement hydration except at high polymer dosages, whereas the performance of NSF and LS in CM blended cement is driven by clinker content.     

Effect of dispersion of sepiolite in sepiolite-NBR composite on the tensile strength

The effect of dispersion of sepiolite in a sepiolite-NBR composite on the tensile strength of the composite was examined. Fibrous sepiolite was ultrasonically treated in distilled water with various types of dispersant. The ultrasonicated sepiolite was mixed with NBR latex to form a sepiolite-NBR complex. The tensile strength of the complex was examined to evaluate the degree of dispersion of sepiolite. The tensile strength results for the composites confirmed that a lower ultrasonication frequency produced a high strength in the composite. The tensile strength actually increased from 3 to 8 MPa as a result of ultrasonication at 28 kHz. To improve and stabilize the dispersion state, five kinds of dispersant were used. The addition of two dispersants in particular, ammonium polycarboxylate and amino alcohol polyphosphate, resulted in an increase of the strength from 8 to 15–16 MPa. When the composites were heated at 450 °C, the strengths of the composites produced with and without the dispersant were approximately 1.4–1.7 and 0.85 MPa, respectively. Thus, the dispersant still affected the strength of the heated samples.     

Calcium sulphate anhydrite based composite binders; effect of Portland cement and four pozzolans on the hydration and strength

The strength, hydration products, microstructure and heat of early hydration were investigated on alternative hydraulic green cements based on calcium sulphate anhydrite partially blended with Portland cement and pozzolans. Four pozzolans of different physical and chemical nature, namely a geothermal waste, silica fume, metakaolin and pulverized fuel ash were characterized. The composite binders showed hydraulic behavior. The use of Portland cement favoured the strength, which was also higher with the incorporation of siliceous nanometric pozzolans compared to the micrometric silicoaluminate pozzolans. The nanoparticles enhanced the early hydration and changed the gypsum morphology promoting denser matrices of hydration products. The geothermal waste pozzolan was the most effective, while one of the composites with metakaolin showed formation of ettringite and strength losses. The heat of hydration of the composites was considerably lower than that of the neat Portland cement.     

氧化石墨烯调控水泥基材料形成大规模规整结构及其性能表征

将制备的GO与减水剂和拌合水超声处理后用于制备水泥基复合材料,研究结果表明,GO纳米片层在水泥基体中达到了均匀分散,水泥水化产物成为了规整形状的多面体状水化晶体,通过其交织交联形成了大规模规整致密的微观结构。当GO掺量为0.03%时,尺寸为30~190nm GO的水泥基复合材料28d时的抗压强度和抗折强度比对照样品分别提高了78.8%和112.7%,尺寸为110~410nm GO的水泥基复合材料的抗压强度和抗折强度分别提高了72.3%和93.9%,水泥基复合材料的耐久性显著提高。同时提出了水泥基复合材料微观结构形成机理。     

含Q相高铝水泥水化性能的研究

在实验室内采用化学原料烧制Q相-CA(CaO·Al2O3)-C12A7(12CaO·7Al2O3)高铝水泥,对所烧制的水泥进行水化性能研究.研究结果表明:Q相-CA-C12A7高铝水泥早期强度高,中后期强度仍在发展且不倒缩.XRD和DTA分析表明,其早期水化产物为铝胶、CAHio和C2AH8,中后期为铝胶、CAH1o、C2AH8和C3AH6.     

Influence of different types of water on strength,porosity and hydric parameters of metakaolin admixtured cement

The present research deals with strength, porosity and hydric behavior of metakaolin cement admixtured with different types of water. The hydration of ordinary Portland cement in the presence of 0%, 10%, 20% and 30% metakaolin treated with distilled, ground and sea water with the water to cement ratio of 0.4 was studied. The experimental results on setting time, strength, porosity and hydric parameters are reported. The results show that, metakaolin percentage increases in strength with a decrease in porosity. The observed results are discussed with SEM micrographs. Further, sea water accelerates the cement hydration at the early stages but retards it in the latter stages of hydration.     

Strength development of ternary blended cement with limestone filler and blast-furnace slag

The benefits of limestone filler (LF) and granulated blast-furnace slag (BFS) as partial replacement of portland cement are well established. However, both supplementary materials have certain shortfalls. LF addition to portland cement causes an increase of hydration at early ages inducing a high early strength, but it can reduce the later strength due to the dilution effect. On the other hand, BFS contributes to hydration after seven days improving the strength at medium and later ages.Mortar prisms in which portland cement was replaced by up to 20% LF and 35% BFS were tested at 1, 3, 7, 28 and 90 days. Results show that the contribution of LF to hydration degree of portland cement at 1 and 3 days increases the early strength of blended cements containing about 5–15% LF and 0–20% BFS. The later hydration of BFS is very effective in producing ternary blended cements with similar or higher compressive strength than portland cement at 28 and 90 days. Additionally, a statistical analysis is presented for the optimal strength estimation considering different proportions of LF and BFS at a given age. The use of ternary blended cements (PC–LF–BFS) provides economic and environmental advantages by reducing portland cement production and CO₂ emission, whilst also improving the early and the later compressive strength.     

Effect of Additives on the Morphology of the Hydrated Product and Physical Properties of a Calcium Phosphate Cement

The morphology of a hydrated calcium phosphate cement （CPC） doped with several normally used additives was investigated by scanning electron microscopy （SEM） and the compressive strength of the cement was determined in this study. The hydrated products of CPC without additives was rod-like hydroxyapatite （HA） grains with around 2-5 μm in length and 100 nm in width. The addition of Sr obviously decreased the crystal size of the rod-like grains. CPCs containing carbonate, collagen and gelatin showed flake-like crystal morphology. Crylic acid-containing CPC presented flocculus-like structure. And malic acid-containing CPC exhibited oriented flake-like structure. The X-ray diffraction （XRD） analysis showed that the additives used in this study did not alter the hydration products of the cement. The compressive strength tests indicated that the compressive strength of the cement with rod-like morphology HA crystals was much higher than that of the cement with flake-like morphology HA crystals, and the cement with oriented flake-like morphology HA crystals exhibited the poorest compressive strength.     

Influence of different types of water on strength, porosity and hydric parameters of metakaolin admixtured cement

The present research deals with strength, porosity and hydric behavior of metakaolin cement admixtured with different types of water. The hydration of ordinary Portland cement in the presence of 0%, 10%, 20% and 30% metakaolin treated with distilled, ground and sea water with the water to cement ratio of 0.4 was studied. The experimental results on setting time, strength, porosity and hydric parameters are reported. The results show that, metakaolin percentage increases in strength with a decrease in porosity. The observed results are discussed with SEM micrographs. Further, sea water accelerates the cement hydration at the early stages but retards it in the latter stages of hydration.     

自感知镍纳米线/水泥基复合材料的制备及压敏性能

通过多孔氧化铝模板交流电沉积的方法制备了镍纳米线,以镍纳米线为导电填料、聚羧酸减水剂为分散剂,首次制备了新型的自感知镍纳米线/水泥基复合材料。通过SEM、TEM和XRD测试方法,研究了镍纳米线与镍纳米线水泥基复合材料的显微结构,与此同时,用四电极伏安法研究了镍纳米线水泥基复合材料的渗流阈值和压敏性。结果显示：所得的镍纳米线直径约为65 nm,长径比约为50;聚羧酸型减水剂能有效提高镍纳米线的分散性;水泥基复合材料的电阻率随镍纳米线的掺量增加呈现渗流特性,渗流阈值为0.5vol%;掺加1.0vol%镍纳米线的水泥基复合材料的应变灵敏度系数高达509.2,远高于电阻应变片的2.0,适用于混凝土结构应力监测的传感元件。