K2O/Na2O对不同水泥基材料早期收缩及开裂的影响

通过外掺Na₂SO₄和K₂SO₄将低热硅酸盐水泥、中热硅酸盐水泥和普通硅酸盐水泥总碱含量调节至1.2%,并使K₂O/Na₂O (质量比)控制在0.4~13.7范围内,探讨了K₂O/Na₂O对3种水泥基材料收缩和开裂的影响。并基于微量热技术、电子显微镜技术和能谱技术,揭示了K₂O/Na₂O对不同水泥基材料收缩和开裂的影响机制。研究表明,随K₂O/Na₂O的增加,低热硅酸盐水泥和普通硅酸盐水泥的自收缩和干燥收缩增加,中热硅酸盐水泥的自收缩和干燥收缩先降低后增加,而不同水泥基材料开裂敏感性始终表现为增加。K₂O/Na₂O引起不同收缩特性的主要原因与水泥基材料水化进程有关,而不同的开裂敏感性,除与收缩性能相关外,还受水泥基材料水化产物水化硅酸钙(C-S-H)、氢氧化钙(CH)形貌及界面过渡区(ITZ)元素富集的影响。     

不同类型盐碱对不同水泥基材料收缩性能的影响

通过分别外掺Na₂SO₄(Na碱)和K₂SO₄(K碱)将低热硅酸盐水泥、中热硅酸盐水泥和普通硅酸盐水泥总碱含量均调节至0.8%和1.2%,探究了不同类型盐碱对不同水泥基材料自收缩和干燥收缩的影响,并基于微量热技术、孔结构分析技术和核磁共振技术,揭示了不同类型盐碱对不同水泥基材料自收缩和干燥收缩的影响机制。研究表明:①盐碱促进了不同水泥基材料的收缩。在相同盐碱含量下,低热硅酸盐水泥具有较低的自收缩率,普通硅酸盐水泥自收缩率最大,但普通硅酸盐水泥干燥收缩最小,中热硅酸盐水泥干燥收缩最大;②在不同水泥基材料中,K碱的促进作用高于Na碱,并随碱含量的增加而增加,当碱含量为0.8%时,K碱的促进作用为Na碱的1.1倍以上,当碱含量为1.2%时,K碱的促进作用为Na碱的1.3倍以上。微观试验表明,K碱较Na碱对水泥基材料收缩具有更高的促进作用,其机制在于K碱能更大程度促进水泥水化,提高影响收缩的＜50 nm的孔含量,并与Al原子向水化硅酸钙(C-S-H)链中转移有关。     

大体积混凝土胶凝材料体系水化放热规律研究

为研究低热硅酸盐水泥与大掺量矿物掺合料胶凝材料体系间水化放热规律方面的差异,采用直接法测定两者的水化放热过程,根据计算出的水化放热曲线及水化速率曲线,分析了两者在水化放热规律方面的差异;并采用Krstulovic-Dabic模型3个时期的积分方程进一步对比分析两者在水化进程方面的差异。研究结果表明试验方案中掺有矿粉的胶凝材料体系水化热前期低于低热硅酸盐水泥,而后期高于低热硅酸盐水泥;在水化放热规律方面,掺入一定掺量的矿物掺合料后,与低热硅酸盐水泥相比,初终凝时间延后,加速期与减速期延长;在结晶成核与晶体生长(NG)时期,n值越大,水化阻力越大,初凝时间相对推后,k_NG值越大,水化速率越快,加速期越短,终凝时间相对提前,在相边界反应时期(I)与扩散时期(D),k_I,k_D越大,水化速率越快,减速期越长。研究结果为改善大体积混凝土的温度防裂性能提供参考。     

甲酸钙对轻烧氧化镁水泥基材料水化和膨胀性能的影响

轻烧氧化镁(LBM)作为一种补偿水工大体积混凝土温降收缩的膨胀剂,其膨胀性能与氧化镁水化密切相关。水工混凝土冬季施工常常要用到早强剂,甲酸钙(CF)是目前应用最广的一种早强剂。关于早强剂对水泥水化影响的研究很多,但是缺乏关于早强剂对掺膨胀剂水工混凝土膨胀性能影响的研究。通过测定凝结时间、水化热、线性膨胀和抗压强度等性能,结合XRD和SEM微观表征,系统地研究了CF对LBM水泥基材料水化及膨胀性能的影响。结果表明,在蒸馏水中,掺CF抑制LBM的水化,延缓了其凝结。然而在水泥基材料中,CF加速了LBM的水化,提升了其膨胀性能。XRD和SEM分析显示,掺入CF促进Ca(OH)₂和C-S-H凝胶生成,从而加速了MgO的水化。     

Na碱和K碱对低热水泥收缩性能的影响

通过分别外掺Na₂SO₄(Na碱)和K₂SO₄(K碱)的方式,将低热水泥的总碱含量提高至0.8%,1.2%和1.6%,研究了不同碱含量和不同碱类型对低热水泥干燥收缩和自收缩的影响,并从水化动力学和孔结构方面,探究了不同碱含量和不同类型碱对低热水泥收缩性能的影响机制。结果表明,碱促进了低热水泥的干燥收缩和自收缩,这种促进作用不可忽略,且对自收缩影响时效短于干燥收缩,而以K₂SO₄形式存在的碱更易促进低热水泥干燥收缩和自收缩。基于水化动力学和孔结构研究,不同类型碱对低热水泥收缩性能的影响机制在于:碱促进了低热水泥结晶成核和晶体生长过程,细化了孔结构,增加了与收缩性能相关的孔分布,而以K₂SO₄形式存在的碱,能使这种促进作用和细化作用更加明显。该研究可为精细化提高混凝土耐久性提供数据支撑。     

水泥-凝灰岩-粉煤灰复合胶凝材料硬化浆体微观结构特征

利用X射线衍射(XRD)、热重(TG)、压汞法(MIP)、扫描电镜分析(SEM)等现代测试技术与方法对水泥-凝灰岩-粉煤灰复合胶凝材料硬化浆体微观结构特征进行测定和分析。结果显示:凝灰岩的掺入使得硬化浆体中引入了长石、水云母及低温型石英(α-SiO₂)等晶相物质,其余水化产物与纯水泥样品基本相同;含有凝灰岩的水泥硬化浆体中Ca(OH)₂含量降低幅度明显小于水泥-粉煤灰二元胶凝体系;随着养护龄期的延长,复合胶凝材料硬化浆体孔隙率逐渐降低,孔径逐步得到细化,到水化180 d时,各样品中最可几孔径的分布主要集中在4.5~50 nm,浆体结构朝着对耐久性有利的方向发展;凝灰岩颗粒特殊形貌引起的形态效应和微集料填充作用在水化初期显得较为明显;相比于同掺量情况下的单掺粉煤灰体系和单掺凝灰岩体系,水泥-凝灰岩-粉煤灰三元胶凝体系的水化产物较多,越来越多的凝灰岩和水泥的水化产物包裹粉煤灰球形颗粒,并逐渐形成整体,整个浆体微观结构结合紧密。     

高贝利特水泥的水化性能研究

对高贝利特水泥的力学性能、凝结时间、水化热以及水化产物类型和微观结构等进行了试验研究,结果表明:高贝利特水泥的早期强度较低,凝结时间较长,水化放热较低;水化产物的类型与硅酸盐水泥相似;水化龄期延长时,浆体中孔隙数量显著减少,孔径细化;水化90 d时,多数孔的孔径为10～60 nm。     

高钛矿渣-水泥复合胶凝材料体系的水化机理研究

采用SEM,XRD,TG-DSC等微观测试手段,探讨掺高钛矿渣-水泥复合胶凝材料体系的水化机理。研究结果表明：高钛矿渣主要由结晶性强的稳定矿物组成,水化活性低;高钛矿渣颗粒分散并填充水泥颗粒,明显改善浆体结构。水化反应早期,硬化浆体结构疏松,水化产物较少,有大量未被反应的稳定晶相。反应后期,Ca(OH)₂参与二次水化反应,强度稳定增长。     

纳米SiO2和碳酸钙晶须制备水泥基材料性能试验

采用纳米SiO₂和碳酸钙晶须制备水泥基材料，利用SEM、XRD和TG-DSC等技术手段对水泥基材料的水化产物、微观结构和热稳定性等进行有效表征，并试验研究了双掺0%、1%、2%、3%、5%、10%的碳酸钙晶须和1%纳米SiO₂保温水泥砂浆的力学性能和导热性能。研究结果表明：纳米-毫米两种尺度材料掺入水泥浆内部后，纳米SiO₂与水泥水化产物Ca(OH)₂晶体发生二次水化反应，生成C-S-H凝胶体，有效地填充水泥基体孔隙、细化水泥基内部孔径尺寸，碳酸钙晶须具备纤维和微粒双重作用，可以在水泥基中产生纤维的桥联效应，两者材料结合起来，可在水泥基内部形成密实网状絮凝结构；纳米SiO₂和碳酸钙晶须掺入后可以提高砂浆的强度，3%碳酸钙晶须和1%纳米SiO₂配制的保温水泥砂浆抗压和抗折强度分别为25.6 MPa和6.19 MPa,导热系数为0.456 7 W/(m·K),强度和导热性能兼顾。     

HAP/Ag3PO4纳米复合物的制备及其对水体有机污染物的降解

以固体废弃物牡蛎壳为原料,利用水热法制备出高纯度的纳米羟基磷灰石(HAP),负载磷酸银(Ag₃PO₄)制备出具有高效光催化性能的HAP/Ag₃PO₄纳米复合物。采用FT-IR、XPS、XRD和SEM对其晶型、化学结构和形貌进行了表征,证实Ag₃PO₄被成功负载在源于牡蛎壳的HAP上。在此基础上研究了HAP/Ag₃PO₄纳米复合物在水污染治理领域的应用,发现模拟日光照射4 min、纳米复合物用量为1.5 g/L、对初始质量浓度为20 mg/L的罗丹明B溶液的降解率达到94.2%,表明制备的HAP/Ag₃PO₄纳米复合物是一种高效光催化剂,可以快速高效地降解水中的有机污染物。     

纳米CuO改性水泥基材料力学与耐久性的试验研究

为了明确纳米CuO对低水胶比水泥基材料力学性能和耐久性的改性作用,采用0. 5%～4%纳米CuO制备水泥基材料,研究其对凝结时间、流动性、力学性能和耐久性的影响,并分析其作用机制。试验结果表明:0. 5%～4. 0%纳米CuO能降低低水胶比水泥基材料的凝结时间和流动性,掺量越多,其降低幅度越大; 1. 0%～4. 0%纳米CuO能提高低水胶比水泥基材料的抗折和抗压强度,但会降低其干燥收缩和渗透性能,掺量以2%为宜;纳米CuO替代水泥后,虽不能参与水泥的二次水化,但能促进水泥的水化;综合分析发现,纳米CuO能发挥尺寸效应、微集料的填充效应和表面活性效应,达到提高水泥基材料密实度和细化孔结构的目的。因此,纳米CuO替代水泥后,能在一定程度上改性低水胶比水泥基材料的力学性能和耐久性。     

Ammonium nitrogen removal from slurry-type swine wastewater by pretreatment using struvite crystallization for nitrogen control of anaerobic digestion.

Precipitation of ammonium together with phosphate and magnesium is a possible alternative for lowering the nitrogen content of wastewater. In this study we examine the removal of ammonium nitrogen and phosphorus from slurry-type swine wastewater containing high concentrations of nutrients by the addition of phosphoric acid along with either calcium oxide or magnesium oxide, which leads to the crystallization of insoluble salts such as hydroxyapatite and struvite. The struvite crystallization method showed a high capacity for the removal of nitrogen when magnesium oxide and phosphoric acid were used as the magnesium and phosphate sources, respectively. When it was applied to swine wastewater containing a high concentration of nitrogen, the injection molar ratio of Mg2+:NH4+:PO4(3-) that gave maximum ammonium nitrogen removal was 3.0:1.0:1.5.     

Struvite crystallization versus amorphous magnesium and calcium phosphate precipitation during the treatment of a saline industrial wastewater

Struvite crystallization (MgNH(4)PO(4)·6H(2)O, MAP) could be an alternative for the sustainable and economical recovery of phosphorus from concentrated wastewater streams. Struvite precipitation is recommended for those wastewaters which have high orthophosphate concentration. However the presence of a cheap magnesium source is required in order to make the process feasible. For those wastewater treatment plants (WWTP) located near the seashore magnesium could be economically obtained using seawater. However seawater contains calcium ions that could interfere in the process, by promoting the precipitation of amorphous magnesium and calcium phosphates. Precipitates composition was affected by the NH(4)(+)/PO(4)(3-) molar ratio used. Struvite or magnesium and calcium phosphates were obtained when NH(4)(+)/PO(4)(3-) was fixed at 4.7 or 1.0, respectively. This study demonstrates that by manipulating the NH(4)(+)/PO(4)(3-) it is possible to obtain pure struvite crystals, instead of precipitates of amorphous magnesium and calcium phosphates. This was easily performed by using either raw or secondary treated wastewater with different ammonium concentrations.     

Enhanced removal of sodium salts supported by in-situ catalyst synthesis in a supercritical water oxidation process

For practical applications of supercritical water oxidation to wastewater treatment, the deposition of inorganic salts in supercritical phase must be controlled to prevent a reactor from clogging. This study investigated enhanced removal of sodium salts with titanium particles, serving as a salt trapper and a catalyst precursor, and sodium recovery by sub-critical water. When Na(2)CO(3) was tested as a model salt, sodium removal efficiency was higher than theoretically maximum efficiency defined by Na(2)CO(3) solubility. The enhanced sodium removal resulted from in-situ synthesis of sodium titanate, which could catalyse acetic acid oxidation. The kinetics of sodium removal was described well by a diffusion mass-transfer model combined with a power law-type rate model of sodium titanate synthesis. Titanium particles showed positive effect on sodium removal in the case of NaOH, Na(2)SO(4) and Na(3)PO(4). However, they had negligible effect for NaCl and negative effect for Na(2)CrO(4), respectively. More than 99% of trapped sodium was recovered by sub-critical water except for Na(2)CrO(4). In contrast, sodium recovery efficiency remained less than 50% in the case of Na(2)CrO(4). Reused titanium particles showed the same performance for enhanced sodium removal. Enhanced salt removal supported by in-situ catalyst synthesis has great potential to enable both salt removal control and catalytic oxidation.     

Microbial effects on phosphorus release in aquatic sediments

Microbial effects on phosphorus release were studied for the sediments of Tianjin source water by controlling DO and pH. The results show that: (1) In sterilised water, phosphorus began to release when pH = 9.1 and the stable release rate was 9.51 mg/(d.m2). It indicates that microorganisms may utilise anaerobic iron respiration to release Fe-P. (2) With unsterilised water, phosphorus release rate is 2.14 mg/(d.m2) when pH = 6.5, 8.60 mg/(d.m2) when pH is uncontrolled, and gets to 8.51 mg/(d.m2) when pH = 9.1. This indicates that microorganisms can dissolve insoluble phosphates to accelerate the ion exchange of OH(-) and PO4(3-), which are derived from iron-bound ortho-P and aluminium-bound ortho-P.     

磷酸镁水泥制备试验研究

基于水工建筑物的应急抢险与快速修补加固处理的需要,运用常规的水泥凝结时间、强度等基本性能试验,研究各材料组成对磷酸镁水泥性能的影响,确定磷酸镁水泥配方,并对不同粒径砂土的磷酸镁水泥砂浆水胶比、养护条件、强度等进行了试验研究。结果表明,硼砂是磷酸镁水泥的有效缓凝剂;氧化镁细度对水泥性能有明显影响,氧化镁越细水泥早期强度越高,但细度过细凝结时间将难以满足施工要求;磷酸镁水泥配方为:P/M值1∶3,硼砂掺量10%,氧化镁细度宜为195 m~2/kg左右;磷酸镁水泥砂浆抗压强度与胶水比具有线性相关性,与龄期呈对数关系;水中养护与标准养护相比,抗压强度降低约6%～27%,磷酸盐水泥在长期水下环境中的适用性需论证。研究成果可为水工建筑物的应急抢险与快速修补加固处理提供参考和依据。     

碱激发高钛矿渣-水泥基胶凝体系水化活性研究

采用丽江42.5中热水泥,攀钢集团水淬高钛矿渣,对Ca(OH)2、NaOH及Na2CO3等碱激发剂激发高钛矿渣的早期活性进行了研究,并探讨了高钛矿渣的化学活化技术及其活化机理,以期为高钛矿渣的综合利用提供理论支持。结果表明：激发剂的掺量不宜过大,最优掺量范围为4%~6%;Ca2+对掺高钛矿渣复合胶凝体系的激发效果较好,且在OH-存在的条件下,早期激发效果更佳。机理分析表明,Ca2+和OH-对高钛矿渣活性的激发,主要是依靠OH-的极化作用,形成具有胶凝作用的水化CaSiO4等产物,且当溶液中Ca2+和SO2+4共存时,能较大程度地激发高钛矿渣的潜在活性。     

Solutions to a combined problem of excessive hydrogen sulfide in biogas and struvite scaling.

The Woodman Point Wastewater Treatment Plant (WWTP) in Western Australia has experienced two separate problems causing avoidable maintenance costs: the build-up of massive struvite (MgNH4PO4. 6H2O) scaling downstream of the anaerobic digester and the formation of hydrogen sulfide (H2S) levels in the digester gas to levels that compromised gas engine operation and caused high operating costs on the gas scrubber. As both problems hang together with a chemical imbalance in the anaerobic digester, we decided to investigate whether both problems could be (feasibly and economically) addressed by a common solution (such as dosing of iron solutions to precipitate both sulfide and phosphate), or by using separate approaches. Laboratory results showed that, the hydrogen sulfide emission in digesters could be effectively and economically controlled by the addition of iron dosing. Slightly higher than the theoretical value of 1.5 mol of FeCl3 was required to precipitate 1 mol of dissolved sulfide inside the digester. Due to the high concentration of PO4(3-) in the digested sludge liquor, significantly higher iron is required for struvite precipitation. Iron dosing did not appear an economic solution for struvite control via iron phosphate formation. By taking advantage of the natural tendency of struvite formation in the digester liquid, it is possible to reduce the risk of struvite precipitation in and around the sludge-dewatering centrifuge by increasing the pH to precipitate struvite out before passing through the centrifuge. However, as the Mg2+/PO4(3-) molar ratio in digested sludge was low, by increasing the pH alone (using NaOH) the precipitation of PO4(3-) was limited by the amount of cations (Ca2+ and Mg2+) available in the sludge. Although this would reduce struvite precipitation in the centrifuge, it could not significantly reduce PO4(3-) recycling back to the plant. For long-term operation, maximum PO4(3-) reduction should be the ultimate aim to minimise PO4(3-) accumulation in the plant. Magnesium hydroxide liquid (MHL) was found to be the most cost-effective chemical to achieve this goal. It enhanced struvite precipitation from both, digested sludge and centrate to the point where more than 95% PO4(3-) reduction in the digested sludge was achieved.