Multi-scale characteristics of magnesium potassium phosphate cement enhanced by waste concrete powder

Using recycled concrete powder (RP) as an alternative binder can effectively reduce construction and demolition waste and contribute to developing eco-friendly repair materials. However, the effect of RP on magnesium potassium phosphate cement (MKPC) has not been sufficiently studied. In this study, MKPC pastes were prepared by replacing different contents of MgO with RP, and the evolution of the structural behavior was explained from nanoscale to microscale. The results show that incorporating an appropriate amount of RP can increase the fluidity and setting time of the MKPC mixture and improve its mechanical properties. The drying shrinkage and water resistance of MKPC specimens also improve with the increasing RP content. Incorporating an appropriate amount of RP can refine the pore structure of MKPC samples, while the generation of gel-like products can compensate for the adverse effects of reduced struvite-K content. The nanoscale characteristics of the MKPC samples also indicate that incorporating RP results in a decrease in the residual MgO and pore phase content, an increase in the content of the hydrated phase, and a decrease in the loss of the hydrated phase volume fraction due to water soaking. Upon optimizing the RP content, the MKPC mixture exhibits a lower cost and carbon footprint, with the 28-d compressive strength of the sample mixed with 10% RP increased by 7.36% relative to the plain sample, indicating that recycling RP is feasible in an eco-friendly MKPC system.     

硼砂/三乙醇胺复合缓凝剂对磷酸钾镁水泥水化硬化性能的影响

磷酸钾镁水泥(MKPC)的速凝特性限制了其在更多工程领域的应用发展，有效延长凝结时间是其工程化应用的关键技术之一。本研究使用硼砂/三乙醇胺复合缓凝剂，深入研究了其对磷酸钾镁水泥凝结时间、抗压强度、物相组成、微观形貌、孔结构和水化放热等特性的影响，并探讨了缓凝机理。结果表明：在保障7 d抗压强度大于20 MPa条件下，复合缓凝剂的使用，可实现26～100 min的凝结时间调控；三乙醇胺分子包覆MgO颗粒，发挥阻水作用，从而显著降低水化反应的标准水化放热速率与标准水化放热量，达到缓凝效果；试样中K-鸟粪石含量的减少与大于10 nm孔隙体积的增加是削弱抗压强度的主要原因。     

海水和矿物掺合料对硫铝酸盐水泥砂浆性能的影响

本文研究了不同拌和水以及海水拌和时粉煤灰和硅灰掺量对硫铝酸盐水泥(SAC)砂浆力学性能和表观孔隙率以及净浆凝结时间、化学收缩、孔溶液pH值和氯离子结合能力等的影响,并通过XRD、SEM和EDS分析水泥水化产物和微观结构。结果表明,海水能加快SAC早期水化并提高其早期强度,但后期强度和淡水拌和时无明显差别。粉煤灰和硅灰均会延长SAC凝结时间,对早期抗压强度不利,而掺加质量分数为5.0%和7.5%的硅灰能提高SAC砂浆28 d抗压强度。硅灰掺量增加时会提高用水量和表观孔隙率,降低流动性,使水泥化学收缩增大,降低净浆pH值且减少氯离子结合量;粉煤灰能够提高砂浆流动性,减少水泥化学收缩,但掺量越大对SAC砂浆抗压强度和抗折强度越不利,掺质量分数为10%的粉煤灰可小幅提高氯离子结合量且减小表观孔隙率。     

Preparation and characterization of a novel magnesium phosphate cement-based emulsified asphalt mortar

To improve the efficiency of repairing asphalt pavements, a rapid-hardening magnesium-based cement emulsified asphalt (MCEA) mortar was developed. The effect of mix parameters on the properties of MCEA sample was systematically discussed, including asphalt to cement (A/C) ratio, asphalt and cement (S/(A+C)) ratio, water to cement (W/C) ratio, and MgO to phosphate (M/P) ratio, as well as the fresh properties, mechanical behavior and microstructure of MCEA sample were investigated. The results show that the initial setting time of MCEA paste is within 30 min, and the fluidity is 60–180 mm, which can effectively improve the efficiency of pavement repair engineering. Meanwhile, by adjusting the mix proportion parameters, the setting time and fluidity can be adjusted according to engineering needs. The compressive and flexural strengths of plain magnesium phosphate cement mortar reach 46.45 and 7.7 MPa, respectively, and they decrease with the increase of A/C, W/C, and M/P ratios. With the increase of S/(A+C) ratio, the area of emulsified asphalt encapsulated particles decreases, which improves the mechanical properties of MCEA mortar. Increasing the A/C ratio results in an increase in the residual MgO content and a decrease in the struvite content in the MCEA paste. Meanwhile, the residual MgO content in the MCEA paste prepared by the S-type emulsified asphalt is significantly lower than that of the N-type MCEA paste, which is related to the water content of the emulsified asphalt. In addition, the incorporation of emulsified asphalt also increases the porosity of the MCEA sample, but the N-type emulsified asphalt can play a role in refining the pore structure of the sample.     

超细矿渣粉和偏高岭土对硫铝酸盐水泥水化和强度的影响

掺入矿物掺合料是改善硫铝酸盐水泥(CSA)混凝土凝结硬化性能和降低生产成本的主要技术途径之一。研究了水胶比为0.4时,单掺超细矿渣粉(UFS)、偏高岭土(MK)与复掺超细矿渣粉、偏高岭土对硫铝酸盐水泥凝结时间、流动度、电阻率、抗压强度的影响,并对其1 d、28 d龄期时的水化产物进行XRD半定量分析。结果表明,单掺和复掺缩短了水泥浆体的凝结时间,但单掺偏高岭土时的缩短效果更明显,且水泥浆体的流动度随着超细矿渣粉和偏高岭土掺量的增加而减小。掺入超细矿渣粉、偏高岭土缩短了水泥浆体电阻率变化速率曲线峰值出现的时间,峰值大小与掺量成递减关系。当掺量从0%(质量分数,下同)增大到20%时,单掺超细矿渣粉试样的28 d抗压强度减小了24.7%,单掺偏高岭土试样的28 d抗压强度减小了17.7%,两者复掺试样的28 d抗压强度减小了17.3%。超细矿渣粉和偏高岭土对水泥水化产物没有明显影响,但促进了硅酸二钙(β-C₂S)的早期水化。     

定型相变材料对磷酸钾镁水泥性能的影响

利用实验室制备的癸酸/膨胀石墨定型相变材料、月桂酸/膨胀石墨定型相变材料和石蜡/膨胀石墨定型相变材料对磷酸钾镁水泥(MKPC)水化温升进行调控,同时研究了定型相变材料对MKPC水泥工作性能、水化热和强度的影响。结果表明:掺入癸酸/膨胀石墨定型相变材料、月桂酸/膨胀石墨定型相变材料后,MKPC的水化过程发生变化,磷酸钾镁水泥的性能改变:凝结时间缩短,流动度减小,水化温峰T_(max)和水化热降低,但强度有较大幅度减小。掺入石蜡/膨胀石墨定型相变材料后,MKPC水化温峰T_(max)随其掺量增加呈规律性降低。较癸酸和月桂酸,石蜡对MKPC水化过程影响较小,石蜡/膨胀石墨定型相变材料的MKPC工作性能更优。     

废弃砂浆粉对水泥物理力学性能的影响

研究了废弃砂浆粉对水泥物理力学性能的影响,测试了标准稠度需水量、凝结时间、流动度和强度.结果表明:废弃砂浆粉的掺加导致水泥的标准稠度需水量增加,水泥的凝结时间总体降低,水泥净浆的流动度及流动度损失均呈降低趋势,而减水剂与水灰比对水泥净浆的流动度及流动度损失有较大影响.废弃砂浆粉掺加量的多少将直接影响到水泥砂浆的强度,掺量越大,水泥砂浆强度损失越严重,而掺量低于10%时,水泥砂浆仍具有较高的抗压强度和抗折强度.微观结构特征表明,废弃砂浆粉掺量在一定范围时,水泥砂浆体系中产生钙矾石与C-S-H凝胶较多,体系结构密实性好.     

Influence of magnesia-to-phosphate molar ratio on microstructures,mechanical properties and thermal conductivity of magnesium potassium phosphate cement paste with large water-to-solid ratio

This paper describes the influence of the magnesia-to-phosphate (M/P) molar ratios ranging from 4 to 12, on the properties and microstructures of magnesium potassium phosphate cement (MKPC) pastes with a large water-to-solid ratio (w/s) of 0.50. The setting behavior, compressive strength, tensile bonding strength and thermal conductivity of the MKPC pastes, were investigated. The results show that an increase in the M/P ratio can slow down the setting reaction, and clearly degrade the mechanical strengths, but clearly improve the thermal conductivity of MKPC pastes. Furthermore, micro-characterizations including X-ray diffraction, scanning electron microscopy and thermogravimetric analysis, on the MKPC pastes reveal that a lower M/P ratio can facilitate better crystallization of the resultant magnesium potassium phosphate hexahydrate (MKP) and a denser microstructure. Moreover, strong linear correlations are found between the mechanical strengths and the MKP-to-space ratio, and between thermal conductivity and the volume ratio of the unreacted magnesia to the MKP.     

Property improvement of Portland cement by incorporating with metakaolin and slag

The physical and mechanical properties of Portland cement (PC) containing metakaolin (MK) or combination of MK and slag and the compatibility between such materials and superplasticizers were investigated in present study. After MK was incorporated into PC, the compressive strength of the blended cement was enhanced. However, the fluidity of MK blended cement became poorer than that of PC at the same dosage of superplasticizer and the same water/binder ratio. When both MK (10%) and ultra-fine slag (20% or 30%) were incorporated into PC together, not only the compressive strength of the blended cement was increased, but also the fluidity of the blended cement paste was improved comparing to MK blended cement. This indicates that ultra-fine slag can improve the physical and mechanical properties of MK blended cement. The physical and chemical effects of two mineral admixtures were also discussed.     

外加剂对硫铝酸盐水泥的影响

针对硫铝酸盐水泥混凝土塌落度损失大、凝结时间不易控制以及浆体不均匀等问题,通过净浆、砂浆试验研究了缓凝剂、减水剂和复合掺合料对硫铝酸盐水泥浆体的凝结时间、浆体流动度及早期、后期强度的影响.结果表明:适当掺量缓凝剂可以有效的控制混凝土塌落度损失、改善施工性能,并可适当提高硬化浆体强度;恰当掺量的减水剂可以在不影响浆体硬化强度的基础上大大提高其流动性;合适比例的粉煤灰和矿渣复掺有利于后期强度的增长并改善其微观结构.     

早龄期磷酸钾镁水泥砂浆的抗冻性评价

为了研究早龄期磷酸钾镁水泥(MKPC)砂浆的抗冻性,测试了在水和5%(质量分数)Na₂SO₄溶液中快速冻融早龄期MKPC砂浆试件的强度、体积变形和吸水率,分析了其物相组成和微观形貌,并将其与水化28 d的MKPC砂浆试件相比较。结果表明,快速冻融循环环境下,早龄期MKPC砂浆试件(水化龄期超过1 d)的强度衰减程度低于水化28 d的MKPC砂浆试件,经受225次冻融循环后,早龄期MKPC浆体试件的剩余强度与28 d水化龄期的MKPC砂浆试件接近,在硫酸盐冻融循环环境下MKPC砂浆试件的强度衰减程度低于水冻融循环环境下的MKPC砂浆试件。早龄期MKPC砂浆试件(水化龄期超过1 d)在冻融循环环境下有较好的抗变形能力,且明显优于水化龄期28 d的MKPC试件。水冻融循环环境下MKPC砂浆试件的抗变形能力优于硫酸盐冻融循环环境下的MKPC砂浆试件。冻融循环过程对水化28 d的MKPC砂浆硬化体孔结构的劣化作用强于水化1 d的MKPC砂浆硬化体。经受硫酸盐冻融循环的MKPC砂浆硬化体的开口孔隙率低于同条件的水冻融循环MKPC硬化体。     

氨基磺酸系高效减水剂ASP缓凝性能研究

氨基磺酸系高效减水剂是一种具有缓凝性能的新型高效减水剂，研究的结果表明：氨基磺酸系高效减水剂ASP分散能力强，流动度损失小，120min内相对流动度损失率仅为7．7％，远小于萘系减水剂FDN；掺加0．5％ASP的水泥净浆初凝和终凝时间较空白分别延长1h 55min和6h 30min，水泥水化放热峰较空白推迟约7h，但不能明显降低水化放热峰值；混凝土28d抗压强度为空白的1．38％，其混凝土试块微结构比掺FDN的试块更为均匀、细密，基本上已看不出网状结构。氨基磺酸系高效减水剂适合配制用于泵送的高强高性能混凝土。     

磷渣对水泥浆体水化性能和孔结构的影响

通过对水泥浆体凝结性能、水化放热、力学性能和孔结构的测定,以及扫描电镜分析和差热-热重分析,研究了不同掺量磷渣对水泥浆体水化性能和微观结构的影响.结果表明:随着磷渣掺量的增加,浆体的凝结时间延长,水化热减少,早期抗压强度下降.但掺磷渣水泥浆体的后期抗压强度已接近或超过了纯水泥浆体的,磷渣掺量的增加对水泥浆体的后期抗压强度影响不显著.浆体中的Ca(OH)2量随龄期的延长而增加并随磷渣掺量的增加而降低.磷渣的活性效应和填充效应的发挥有效地改善了浆体水化后期的微观结构和孔结构,从而使浆体的力学性能有所提高.     

接枝磺化木质素高效减水剂的配伍性能研究

以酸析木质素为原料,通过接枝、磺化和缩合制得接枝磺化酸析木质素GSAL,研究了它与木质素磺酸盐和消泡剂的配伍性能。结果表明:GSAL分别与木质素磺酸盐及其改性产品复配,可得到减水剂GSAL1和GSAL2。当水灰比为0.29、掺量w(GSAL1)=0.6%时,水泥净浆流动度达243mm;掺量w(GSAL2)=0.8%时,水泥净浆初凝时间延长110min,终凝时间延长约7h。掺量w(GSAL1)=0.8%时,水泥净浆减水率为21.4%,砂浆3d和7d的抗压强度比分别为163%和143%,其对水泥的减水增强作用超过了萘系高效减水剂FDN。GSAL与消泡剂的复配产品起泡性降低,水泥净浆流动度、新拌砂浆密度和砂浆抗压强度比均增大,GSAL与磷酸三丁酯配伍后的综合性能最佳。     

Effect of water content on microstructure and properties of magnesium potassium phosphate cement pastes with different magnesia-to-phosphate ratios

Magnesium potassium phosphate cement (MKPC) is a class of chemically bonded ceramic for special engineering applications. The selection of mass ratios of MgO-to-KH₂PO₄ (M/P) and water-to-cement (W/C) is an important aspect for formulating MKPC paste. This paper analyzed the stoichiometry of the primary reaction of MKPC and investigated the effect of W/C (0.14–0.40) on paste microstructure and properties at different M/P (1.5–4). At high M/P, low W/C was sufficient to complete the hydration of KH₂PO₄ and higher W/C yielded looser microstructure, dictating that properties of high M/P pastes were monotonic functions of W/C. However, a clear W/C threshold effect was found in medium M/P pastes at both micro- and macro-levels. Low W/C below stoichiometric value suppressed the formation of K-struvite and favored the presence of an amorphous phase, leading to intense early shrinkage, low early compressive strength, and poor long-term water resistance. The increase in W/C above stoichiometric value resulted in the segregation of excess water and thus to porous structure, with detrimental effects on dimensional stability and strength. The micro–macro analysis highlighted the importance of stoichiometric water amount in the optimal design of MKPC.     

不同溶液长期浸泡下大流动性磷酸钾镁水泥基防腐涂层的性能

为了探究大流动性磷酸钾镁水泥(MKPC)基防腐涂层在不同溶液环境下的性能,将大流动性磷酸钾镁水泥浸泡于淡水、5%硫酸钠溶液及3.5%氯化钠溶液(同为质量分数)三种腐蚀环境下,测试其强度、干缩率、吸水率,从而建立长期浸泡下性能劣化规律模型,并且以SEM-EDS、XRD对MKPC基防腐涂层在长期浸泡下的腐蚀机理进行分析。结果表明大流动性MKPC在淡水环境下耐腐蚀性能较好,在3.5%氯化钠溶液和5%硫酸钠溶液环境下耐腐蚀性能更好。     

颗粒形貌对水泥性能的影响

以多组水泥样品为对象,在控制其颗粒级配、比表面积基本一致的条件下,利用扫描电镜等测试手段,研究水泥颗粒形貌改善对水泥性能及孔结构等的影响。结果表明：水泥颗粒形貌改善后,水泥胶砂流动度随水泥颗粒形貌的改善而不断增大。水泥凝结时间略有延长,水泥颗粒粉状物料堆积状况更趋密实。水泥胶砂试体中总孔隙率降低,中位孔径及平均孔径减小。在相同砂浆流动度下,颗粒形式改善后水泥的圆形系数由0．67提高至0．72,水灰比可减少8％,各龄期水泥抗压强度均提高20％以上。在相同水灰比下,圆形系数的平均值由0．65提高至0．73,水泥中后期抗压强度平均增长10％～12％。     

Effect of admixture on hydration of cement, adsorptive behavior of admixture and fluidity and setting of fresh cement paste

The adsorptive behavior of admixtures and the hydration of cement in the presence of admixtures were examined and the relationships of them with the physical properties of fresh cement paste including fluidity, variation of fluidity with time and setting time were discussed with the quantitative determination of organic admixture adsorbed on the cement, and with the observation and determination of the surface microstructure and composition of polished clinker dipped in aqueous solution containing a specified quantity of admixture by advanced method of surface analysis.

In order to prepare the same fluidity of fresh cement paste, mortar and concrete, the required amount of an easily adsorbed admixture is larger than that of a hard adsorbed one. An admixture having a functional group producing a complex salt with Ca²⁺ decreases the concentration of Ca²⁺ in liquid phase at early age and delays the saturation of Ca²⁺, which influences the morphology of hydrate produced, causes fluidity loss with time and delays the setting time of cement. The microstructural and compositional estimations of the adsorption layer of admixture on the surface of clinker minerals by in-lens FESEM, ESCA-imaging, AES and AFM indicates that the admixture is partially adsorbed to the interstitial phase in a thick layer, forming characteristic three dimensional surface structure.     

Influence of metakaolin on the conversion and compressive strength of quaternary phase paste

Application of calcium aluminate cement in construction faces the challenges of high manufacturing cost and volumetric instability associated with hydrates conversion. This work introduces a newly developed high-performance Ca₂₀Al₂₆Mg₃Si₃O₆₈ (Q phase)-metakaolin (MK) composite binder. The influence of MK on the conversion and strength development of Q phase paste cured at 40°C was investigated. The mechanism of MK on the stability of synthetic hydrate was studied by solution chemistry, XRD, and NMR. The pure Q phase paste experiences a significant strength reduction due to hydrates conversion, whereas the Q phase paste containing 15% MK exhibits a continuous increase in strength. MK promotes the formation of CAH₁₀, contributing to the refinement of pore structure and enhanced mechanical property. The Al^V and Al^IV dissolved from MK increase the concentration in the pore solution, and then the solubility of CAH₁₀ decreases due to the common-ion effect, thus inhibiting the subsequent precipitation of C₃AH₆. In addition, the release of dissolved alumina from MK considerably impedes silica dissolution, and consequently, the formation of C₂ASH₈ is hindered at a higher content of MK.     

复合缓凝剂对高强磷酸镁修补砂浆性能的影响

本文研究了一元缓凝体系和二元复合缓凝体系对高强磷酸镁修补砂浆凝结时间、流动性能和力学性能的影响。结果表明:在一元缓凝体系中,与硼砂和三聚磷酸钠相比,单掺蔗糖的缓凝效果最优,但蔗糖掺量过高会显著降低磷酸镁修补砂浆的流动性能和早期力学性能;在二元复合缓凝体系中,硼砂和蔗糖组成的二元缓凝体系的缓凝效果优于硼砂和三聚磷酸钠组成的二元缓凝体系,在硼砂5%(质量分数)和蔗糖2.5%(质量分数)时,磷酸镁修补砂浆的凝结时间达到18 min,流动度为230 mm,1.5 h、3 d和28 d强度分别为22.6 MPa、56.8 MPa和62.4 MPa,实现了磷酸镁修补砂浆在凝结时间和早期强度之间的动态平衡。