Prediction of compressive strength of cement mortars with fly ash and activated coal gangue

The pozzolanic activity of coal gangue, which is calcining at 500 to 1 000 ℃, differs distinctly. The simplex-centroid design with upper and lower bounds of component proportion is adopted to study the compressive strength of mortars made with ternary blends of cement, activated coal gangue and fly ash. Based on the results of a minimum of seven design points, three special cubic polynomial models are used to establish the strength predicating equations at different ages for mortars. Five experimental checkpoints were also designed to verify the precision of the equations. The most frequent errors of the predicted values are within 3%. A simple and practical way is provided for determining the optimal proportion of two admixtures when they are used in concrete.

Effect of Coal Gangue with Different Kaolin Contents on Compressive Strength and Pore Size of Blended Cement Paste

The effects of activated coal gangue on compressive strength, porosity and pore size distribution of hardened cement pastes were investigated. Activated coal gangue with two different kaolin contents, one higher and one lower, were used to partially replace Portland cement at 0%, 10%, and 30% by weight. The water to binder ratio（w/b） of 0.5 was used for all the blended cement paste mixes. Experimental results indicate that the blended cement of activated coal gangue mortar with higher kaolin mineral content has a higher compressive strength than that with lower kaolin mineral content. The porosity and pore size of blended cement mortar were significantly affected by the replacement of activated coal gangue.

Pozzolanic Activity of Burned Coal Gangue and Its Effects on Structure of Cement Mortar

The pozzolanic activity of coal gangue burned at different burning temperatures was investigated. The burned coal gangue was mixed with portland cement in different proportions （ 20% - 60% ）. The pozzolanic activity of coal gangue burned and the hydration products were examined, the compressive strengths of the pastes of the mixtures were tested, and the mechanism of the reaction was discussed. The experimental results slum, that the coal gangue burned at 750 ℃ has the optimum pozzolanic activity, and the burned coal ganguc with SiO2 and Al2 O3 is in an active form. When the coal gangue burned at 750℃ is mixed into portland cement, the content of calcium hydroxide in paste is significantly reduced, while the contents of hydrated calcium silk.ate and hydrated calcium aluminate are increased accordingly, hence resulting in the improvement of the microstructure of mortar. The compressive strength of cement paste decreases with increasing the content of burncd coal gangue. The decease in strength is small in the range of 20% - 30% coal gangue substitution and significant in 30%- 60% substitution.

Hydration process in Portland cement blended with activated coal gangue

This paper deals with the hydration of a blend of Portland cement and activated coal gangue in order to determine the relationship between the degree of hydration and compressive strength development.The hydration process was investigated by various means:isothermal calorimetry,thermal analysis,non-evaporable water measurement,and X-ray diffraction analysis.The results show that the activated coal gangue is a pozzolanic material that contributes to the hydration of the cement blend.The pozzolanic reaction occurs over a period of between 7 and 90 d,consuming portlandite and forming both crystal hydrates and ill-crystallized calcium silicate hydrates.These hydrates are similar to those found in pure Portland cement.The results show that if activated coal gangue is substituted for cement at up to 30%(w/w),it does not significantly affect the final compressive strength of the blend.A long-term compressive strength improvement can in fact be achieved by using activated coal gangue as a sup-plementary cementing material.The relationship between compressive strength and degree of hydration for both pure Portland cement and blended cement can be described with the same equation.However,the parameters are different since blended cement produces fewer calcium silicate hydrates than pure Portland cement at the same degree of hydration.

Effect of temperature on the hydration process and strength development in blends of Portland cement and activated coal gangue or fly ash

This paper describes the results of an investigation into the effect of the variation of curing temperatures between 0 and 60 °C on the hydration process,pore structure variation,and compressive strength development of activated coal gangue-cement blend(ACGC) . Hardened ACGC pastes cured for hydration periods from 1 to 360 d were examined using the non-evaporable water method,thermal analysis,mercury intrusion porosimetry,and mechanical testing. To evaluate the specific effect of activated coal gangue(ACG) as a supplementary cementing material(SCM) ,a fly ash-cement blend(FAC) was used as a control. Results show that raising the curing temperature accelerates pozzolanic reactions involving the SCMs,increasing the degree of hydration of the cement blends,and hence increasing the rate of improvement in strength. The effect of curing temperature on FAC is greater than that on ACGC. The pore structure of the hardened cement paste is improved by increasing the curing temperature up to 40 °C,but when the curing temperature reaches 60 °C,the changing nature of the pore structure leads to a decrease in strength. The correlation between compressive strength and the degree of hydration and porosity is linear in nature.

热活化煤矸石对水泥基材料性能影响研究

将热活化煤矸石用作辅助胶凝材料,替代部分水泥,制备水泥砂浆,研究热活化煤矸石掺量对水泥砂浆抗压强度和抗折强度的影响,及热活化煤矸石增强水泥基材料机械强度的机理。结果表明,在利用热活化煤矸石替代部分水泥制备砂浆过程中,适量热活化煤矸石具有良好的火山灰效应和微集料效应,可促进砂浆基体中相互交联网状C—S—H凝胶的形成,增强砂浆基体中孔隙的填充效果,改善砂浆基体的微观结构,进而提升水泥基材料机械强度。当热活化煤矸石掺入量为20%时,砂浆试样水化28 d的抗压强度可达46.2 MPa,抗折强度达6.79 MPa,其机械强度与纯水泥砂浆相当,完全可以满足一般建筑行业使用要求。

煤矸石与气化渣协同作为水泥掺合料的性能影响研究

煤矸石和气化渣是煤炭工业利用过程的副产品,堆存和填埋处置对环境已造成严重的污染和危害。为实现固体废物的资源化利用,基于对煤矸石碱溶液离子快速溶出评价、气化粗渣活性分析等样品分析,采用净浆流动性、胶砂试件的抗压强度与抗折强度、SEM图形分析等多种活性评价方法以确定煤矸石最佳活化温度,即采取胶砂强度试验对煤矸石及气化渣协同作为水泥掺合料对胶砂试件的性能影响规律进行研究。结果表明煤矸石的最佳活化温度为750℃,将活化后煤矸石与机械活化后的气化粗渣进行互配,以30%掺量替代P.O 42.5水泥,得出相较于活化煤矸石单一掺入水泥,煤矸石及气化粗渣协同作为水泥掺和料不但能提高复合胶凝材料的力学性能且对节能减排放起到良好作用。

基于煤矸石混凝土正交试验的试验研究

目前,煤矸石是我国年排放量和累计堆存量最大的工业废弃物之一,有文献研究发现,煤矸石粉碎后,其可以部分或全部代替黏土组分生产普通水泥。该研究以煅烧过的煤矸石粉与非煅烧过的煤矸石粉为研究对象,在混凝土中利用煤矸石替代一部分水泥,来研究混凝土的抗压强度。通过正交试验,发现煅烧过的煤矸石粉活性大于未煅烧的,且煅烧过煤矸石替代水泥的最佳替代范围大致在20%~35%;未煅烧过煤矸石替代水泥的最佳替代范围大致在15%~30%。这个研究结果实现对煤矸石的再利用,具有保护环境和节约资源的重要意义。

煤矸石热活化及相变分析

系统研究了不同温度下热处理活化煤矸石的物相组成和活性组分溶出的变化规律。用差热分析、X射线衍射、红外光谱、核磁共振、电感耦合等离子原子发射光谱和扫描电镜等仪器测试分析煤矸石原矿和不同煅烧温度制备的样品的矿物组成、分子结构、29Si和27Al化学位移、活性Si4+和Al3+溶出量及微观结构。结果表明:煤矸石的活化程度随不同温度下矿物相组成及铝配位情况的变化而改变。连续性的相转变与活性硅、铝的溶出量相对应。

煤矸石热活化及影响因素

对煤矸石热活化及在不同条件下影响其活性的因素进行了系统的实验研究.考察了煅烧温度、粒径形态、停留时间、冷却方式等因素对煤矸石活化的影响.并采用X射线衍射(XRD)、差热(DTA)、红外(FTIR)、电感耦合等离子原子发射光谱仪(ICP-AES)等分析方法深入地了解煤矸石的活化情况.结果表明,煤矸石热活化不仅与关键因素煅烧温度有关,还受到原矿特性、粒径形态、停留时间、冷却方式等因素的显著影响.

活化煤矸石在水泥砂浆中的应用研究

同时采用煅烧、机械细磨和添加化学激发剂三种手段加工处理煤矸石,采用力学性能测试研究了水泥砂浆的强度,通过XRD分析了煤矸石的成分和结构。试验结果表明,经复合加工处理后,煤矸石活化效果明显,得到的活化煤矸石掺混水泥胶砂强度较高。水玻璃的加入可进一步提高煤矸石的活性。经700℃煅烧,水玻璃加入量为1%样品的砂浆强度最高。

煤矸石掺合料的制备及对混凝土碱-骨料反应影响

通过强度评价法,研究了煅烧温度、恒温时间及冷却方式三种热处理技术对未燃煤矸石活性的影响,并将制备的煤矸石掺合料与粉煤灰、矿粉进行了性能对比。在此基础上,通过胶砂流动度和快速砂浆棒试验,研究了煤矸石掺和料的细度、掺量对其稠度和碱-骨料反应的影响。试验结果表明:机械和热活化的煤矸石粉具有微集料和活性效应,对拌合物稠度有一定的改善作用,对混凝土膨胀有一定的抑制作用,其中细度比掺量影响的权重大。当地煤矸石在750℃下煅烧3 h、细度达到1150 m2/kg且掺量控制在5%时,煤矸石掺和料对工作性的改善,以及混凝土碱-骨料反应膨胀抑制效果最好。

煤矸石的热活化工艺研究

通过工艺实验、添加煤矸石水泥胶砂的强度测试、煅烧前后煤矸石成分及结构的XRD分析,研究了煅烧工艺条件对铜川某煤矿煤矸石火山灰活性的影响,探讨了热活化机理以及添加烧煤矸石能够提高水泥胶砂强度的原因,即煤矸石原来排列有序的晶体结构被打乱,形成热力学不稳定状态玻璃相结构,从而使烧成后的煤矸石中含有大量的活性氧化硅和氧化铝,而具有火山灰活性。实验发现所用煤矸石的最佳煅烧温度为700℃,此时水泥胶砂具有最高的抗压和抗折强度。

用活化煤矸石制备新型胶凝材料

采用脱硫石膏和分析纯CaO作为活性激发剂,通过3种方式活化北京房山煤矸石,并检测、分析用不同方式活化的煤矸石制成的胶凝材料的强度,进而研究了活性激发剂和混磨方式对试验材料热蚀变活化的影响。运用X射线衍射分析表征了煤矸石活化前后的微观特性;运用胶砂试块强度分析和扫描电镜(SEM)分析表征了煤矸石质胶凝材料的胶凝活性。结果表明:该煤矸石的主要活性来源是粘土类矿物,700℃煅烧时煤矸石中的高岭石和绿泥石脱水、分解,生成无定形SiO2和Al2O3,与CaO发生固相反应,湿混工艺下固相反应完全,生成C12A7和C2S两种水硬性活性物质,活化物料具有较高的胶凝活性。

煅烧煤矸石粉对混凝土工作性和强度的影响

将小于5mm方孔筛的未燃煤矸石颗粒以不同温度、不同粉磨时间为间隔取点煅烧及粉磨,分别以30%取代水泥,以胶砂强度较高者确定煤矸石最佳的煅烧温度和粉磨时间。在此基础上采用正交试验,研究煅烧煤矸石粉、粉煤灰和矿粉复掺的相容性及对混凝土工作性和强度的影响。结果表明,清河门矿未燃煤矸石最佳煅烧温度750℃、最佳粉磨时间3min;煅烧煤矸石粉、粉煤灰和矿粉之间的不同品种复掺对混凝土拌合物工作性影响特别显著,对7d强度影响显著,对28d强度影响不明显。而掺量比例对工作性和28d强度影响不明显,对7d强度有一定影响。煅烧煤矸石粉与粉煤灰复掺的相容性最好,二者复合使用,既能改善混凝土拌合物工作性,又能保证混凝土7d和28d强度。

固废煤矸石的活化及其对混凝土力学性能的影响

研究表明热力活化和机械活化方法能够有效的提高煤矸石的活性。煤矸石的最佳活化煅烧温度为900℃,煅烧后的煤矸石具有良好的易磨性,粉磨至比表面积550 m2/kg左右为宜。高温煅烧使煤矸石结构膨胀及部分成分挥发,出现较为明显的颗粒状结构并伴有一定的孔洞结构。煤矸石掺合料的需水量较粉煤灰和矿粉高,煅烧煤矸石粉对混凝土有早期的增强作用,且具有后期的强度增长保持能力;其活性介于粉煤灰和矿渣之间,比较接近矿渣。

煤矸石的热力-化学复合活化研究

采用不同温度下的煅烧和添加化学激发物质的复合活化方法对煤矸石用作高性能水泥辅助性胶凝材料时潜在活性激发效果进行了实验探讨。实验结果表明，原始煤矸石未经任何处理直接用作水泥混合材时基本上不表现出火山灰活性，会导致水泥强度大幅度降低。煤矸石经600～900℃加热处理之后再与水泥混合使用，表现出显著的火山灰活性，水泥强度得到明显改善。用芒硝或水玻璃作为激发荆对煤矸石施加热力-化学复合活化，在适宜的掺量范围内水泥强度，尤其是早期强度，得到进一步改善。采用水玻璃的场合活化效果优于采用芒硝的场合。煤矸石热力一化学复合活化的适应范围为热处理温度600～800℃，水玻璃掺量不超过4％。

石灰对煤矸石水泥砂浆性能影响研究

将铜川煤矸石进行热活化和机械活化后,加入石灰进行化学激发,掺入水泥砂浆中进行强度测试,对石灰和煤矸石掺量进行了实验研究,分析了石灰对煤矸石水泥砂浆的作用。结果表明,煤矸石和石灰掺入对水泥砂浆的强度具有较大的影响。煤矸石水泥砂浆的早期抗压和抗折强度均较低,但28 d强度随煤矸石和石灰用量增加出现先增加后降低的趋势。在煤矸石用量达到40%,石灰取代量为40%左右时,水泥砂浆抗压和抗折强度出现最大值。石灰的加入对煤矸石水泥砂浆的强度具有较大的提升作用,掺石灰后,煤矸石水泥砂浆28 d抗压强度提高约21%,抗折强度提高约31%。

化学激发煤矸石对水镁石纤维水泥砂浆性能影响

选取铜川煤矸石进行研究,采取热活化、机械活化和化学活化并用的方式,且在煅烧前将煤矸石与石灰混合,并加入固定量水镁石纤维制成水泥砂浆,通过强度、流动性等力学性能测试和SEM微观测试找出了最优的工艺参数。试验表明:当煅烧温度为675℃,石灰和煤矸石取代水泥量的30%,其中石灰占煤矸石量的40%时,强度和流动性达到最佳值。和普通水泥砂浆相比基本持平,与单一热活化煤矸石水泥砂浆相比强度有大幅度提高。有利于工业废渣的利用和节能减排的进行。

活化煤矸石酸浸过程中金属离子的溶出

以HCl作为酸浸介质,考察热活化及碳酸钠助剂+热活化耦合活化两种活化方式下,煤矸石物料在酸浸过程中Al,Fe,Ca,Mg,K和Ti等金属离子的溶出活性,采用X射线衍射光谱(XRD)和红外光谱(IR)对活化前后的物料及酸浸渣进行矿物组成和微观结构表征,并根据金属在煤矸石中的矿物存在形态对金属离子的溶出活性进行解释.结果表明,在750℃热活化作用下,煤矸石中Al,Fe,Ca和Mg大量溶出,K的溶出率很低,Ti基本上不溶出;加碳酸钠助剂活化不仅有利于Al的溶出,同时滤液中金属离子K,Ti和Na也大量溶出,增加了滤液分离提纯和铝产品制备的难度.此外还研究了煤矸石热活化-酸浸工艺过程中金属离子的溶出规律,提出了酸浸预除杂的措施.