碳化对海砂混凝土中氯离子扩散的影响

选取海阳海砂、淡化海阳海砂和河砂三种细骨料,分别制备强度等级为C30和C50的混凝土,进行加速碳化与氯离子侵蚀复合试验的研究,测出混凝土试块不同深度的水溶性自由氯离子含量.结果表明:海砂混凝土、淡化海砂混凝土在碳化与氯离子侵蚀复合作用下的破坏规律与河砂混凝土基本一致.碳化时间对各种混凝土中氯离子的扩散影响都很大.混凝土强度等级,海砂中固有的氯离子等因素也影响混凝土各深度的水溶性自由氯离子含量.     

淡化海砂高性能混凝土氯离子渗透性研究

针对海砂、淡化海砂和河砂不同细骨料配制的 12组共 36块C6 0和C80高性能混凝土 ,通过基于ASTMC12 0 2标准的通电法氯离子渗透性试验 ,对比分析了淡化海砂高性能混凝土抗渗性随龄期、外掺料和强度等级的变化规律 ,得出了在保证淡化海砂质量的前提下淡化海砂高性能混凝土具有良好耐久性的结论。     

海砂对混凝土耐久性能影响规律的研究

为研究海砂混凝土的耐久性能,制作不同掺量矿粉的河砂、淡化海砂和原状海砂混凝土,对三类混凝土进行碳化、渗透性和钢筋腐蚀试验。试验结果表明,原状海砂不能直接用于钢筋混凝土结构,淡化海砂混凝土的耐久性与河砂混凝土相近,是较理想的建筑材料。     

利用海砂制备高性能混凝土试验研究

研究了细集料砂对水泥胶砂性能的影响,并以海砂为细骨料制备高性能混凝土,分别进行了C60、C100等级海砂高性能混凝土工作性能、力学性能以及耐久性能试验研究。结果表明:海砂水泥胶砂抗压强度比河砂低,但是抗折强度要高于河砂;海砂制备同等级高性能混凝土的工作性、28 d抗压强度及劈裂抗拉强度要优于天然河砂,且早期强度发展迅速;采用电通量法和NEL法评价的氯离子渗透性都处于很低的水平,为海砂混凝土的研究与应用提供了研究基础,为制定海砂混凝土应用技术规范提供重要参考。     

利用海砂配制混凝土的试验研究

利用海砂及淡化海砂配制混凝土并与河砂混凝土进行对比,发现在相同配合比条件下,淡化海砂混凝土与河砂混凝土的工作、力学、耐久性能较为接近,而使用海砂配制的混凝土的各项性能均较差。实验表明淡化处理的海砂配制混凝土性能与河砂较为接近,可以应用于建筑工程中,而直接使用海砂配制的混凝土工作、力学、耐久性能均较差,为保证工程质量,应严禁将海砂直接应用于工程建设。     

淡化海砂混凝土中钢筋的锈蚀特征

采用电化学法分析了不同强度等级的海砂混凝土与淡化海砂混凝土内的钢筋锈蚀发展规律。结果表明,随测试龄期延长,2种混凝土内钢筋腐蚀电位的绝对值为先减小后增大,腐蚀电流密度逐渐增大,且相同强度等级的淡化海砂混凝土内钢筋的腐蚀发展明显慢于海砂混凝土。海水侵蚀对钢筋锈蚀的长期影响大于NaCl溶液;此外,虽然海砂引入了氯离子,但外界环境侵入的氯离子仍是引起钢筋锈蚀的主要原因。     

压制成型海砂混凝土路面砖力学性能试验研究

压制成型混凝土路面砖具有广泛的应用场景。鉴于河砂资源的短缺,且混凝土路面砖中未配置钢筋,直接采用未淡化的海砂用于混凝土路面砖的生产。为了验证其可行性,对不同配合比的路面砖在3 d, 7 d, 14 d和28 d抗压强度和抗折强度进行了测试。试验结果表明,压制成型混凝土路面砖抗压强度随龄期增长较快,3 d即可达到28 d强度的75%左右,14 d可达到90%以上;直接使用未淡化海砂制作的路面砖,其抗压强度较使用淡化海砂的路面砖高约10.5%,抗折强度则与使用淡化海砂的路面砖比较接近。     

原状机制砂混凝土的氯离子渗透与碳化性能试验研究

试验研究了机制砂原料形态、石粉含量对原状机制砂混凝土氯离子渗透和碳化性能的影响,同时测定了相应的新拌混凝土工作性能和硬化混凝土的立方体抗压强度,机制砂原料形态为碎石和卵石,石粉含量为5％、9％和13％,混凝土强度等级为C30、C40、C50和C60.结果表明:新拌混凝土工作性能良好,硬化混凝土抗压强度均达到了设计强度等级的配制要求;氯离子扩散系数和碳化深度均随着混凝土强度的提高、水灰比的降低而减小,碎石破碎的原状机制砂配制的混凝土具有更好的抗氯离子扩散和抗碳化能力;石粉含量增加对原状机制砂混凝土的氯离子扩散和碳化性能影响较小,不同机制砂原料形态时的影响与水灰比和用水量相关.     

海水海砂高性能海工混凝土力学及早期工作性研究

使用海水、海砂代替传统的河水河砂制备混凝土,制备出一种早强低自收缩、高流动度低黏度的海水海砂高性能混凝土。相比河水河砂混凝土,海水海砂的使用可以使水化更充分,加速水化使混凝土具备较高的早期强度;海水海砂混凝土自收缩量降低了15%,收缩结束时间提前,减少了混凝土裂缝的产生;海水海砂混凝土黏度值为7 590 MPa·s,流动度为182 mm,降低了混凝土的黏度增加了流动度,使混凝土更易于泵送,降低了施工难度。28 d抗压抗折强度比使用河水河砂制备的混凝土分别降低了8.6%和25.4%;热水养护可以提高海水海砂混凝土的力学性能,其抗压、抗折强度分别提高了22.8%和23.1%。海水海砂混凝土孔隙液pH与河水河砂混凝土基本相同;使用热水养护会降低混凝土的孔隙液pH,最小值12.0111.50(钢筋钝化膜破坏的临界值)。研究了海水海砂制备高性能混凝土的力学与早期工作性能,为海水海砂混凝土的推广应用奠定了理论基础。     

GFRP筋海砂混凝土梁受弯性能试验研究

河砂过度开采对生态环境造成了严重的影响,用海砂代替传统混凝土中的河砂,可以解决河砂资源缺乏的问题。但是海砂中含有大量的氯离子,对钢筋具有很强的腐蚀性,而纤维增强复合材料(Fiber reinforced polymer,FRP)具有优良的耐腐蚀性,能很好地与海砂混凝土共同工作。为探索GFRP筋海砂混凝土梁受弯性能,文中对4根GFRP筋海砂混凝土梁进行受弯试验,获得混凝土强度和配筋率对海砂混凝土梁的裂缝发展、开裂荷载和极限荷载的影响规律,结果表明提高混凝土的强度等级,对开裂荷载有显著的提升;试验梁的配筋率接近界限配筋率时,混凝土强度等级对极限荷载没有影响,同时试验梁以纯弯段为主裂缝;当配筋率远大于界限配筋率时,提高混凝土强度等级,试验梁的极限荷载有明显的提升,同时试验梁以斜裂缝为主裂缝,通过试验为GFRP筋海砂混凝土梁的设计提供参考。     

Dredged marine sand in concrete: An experimental section of a harbor pavement

This research work describes three experimental sections of a harbor pavement made with three different concretes. The influence of dredged marine sand (DMS) from Port of Sant Carles de la Ràpita (Tarragona, Spain) as a fine aggregate on the production of concretes was analyzed, and its properties were determined. The three concretes were produced at a homologated plant (UNILAND): C1 (control concrete), C2 (concrete made with DMS as corrective fine sand) and C3 (concrete made with DMS as corrective fine sand and reinforced with plastic fibers PF). The fresh and hardened properties of concretes made with DMS approached the results of the control concrete.     

Effect of limestone fines content in manufactured sand on durability of low- and high-strength concretes

This paper investigates the effect of limestone fines content in manufactured sand (MS) on compressive strength, chloride ion permeability and freeze–thaw resistance of both low- and high-strength concretes. The abrasion resistance of concretes and sulfate attack of mortars were also tested. The results show that for low-strength concretes, the increment of limestone fines from 0% to 20% improved the resistance to chloride ion penetration, but decreased the resistance to freezing. For high-strength concretes, the increment of limestone fines from 0% to 15% did not affect the chloride ion permeability and freeze–thaw resistance. Furthermore, the sulfate resistance was increased by the increment of limestone fines, and the amount of 7% and 10% fines resulted in the highest abrasion resistance. It can be concluded that the durable concretes can be made from MS with at least 10% limestone fines.     

Durability of copper slag contained concrete exposed to sulfate attack

Sulfate attack is one of several chemical mechanisms of concrete deterioration. Exposure of concrete structures in the sulfate environments may lead to detrimental chemical, microstructural, and physical changes in the concrete matrix, resulting in serious deteriorations and service life reduction. Partial replacement of cement with slag is one of the efficient methods for improving concrete resistance against sulfate attack. In this paper the performance of copper slag contained concrete in sulfate solution is investigated. In this regard, an experimental study including expansion measurements, compressive strength degradation and microstructural analysis were conducted in sulfate solution on concretes made by replacing 0%, 5%, 10% and 15% of cement with copper slag waste. The results of this study emphasized the effectiveness of copper slag replacement in improving the concrete resistance against sulfate attack.     

不同粗细骨料组合下的混凝土耐硫酸腐蚀研究

为比较不同粗细骨料组合对混凝土耐硫酸腐蚀性能的影响,对水灰比为0.45、尺寸为100×200的4种骨料组合（青石+黄砂,青石+大理砂,大理石+黄砂,大理石+大理砂）混凝土试件进行耐硫酸加速腐蚀试验。将混凝土试件浸泡于pH值为0.95左右的硫酸溶液中进行为期194 d的12次跟踪监测,根据检测数据计算得到了混凝土的腐蚀深度,按线性方程斜率从大到小对4种骨料组合混凝土硫酸腐蚀速率进行了排序。结果表明:含有大理石或大理砂骨料的混凝土比含青石和黄砂骨料的混凝土耐硫酸腐蚀性能高;腐蚀层受扰动情况下,腐蚀深度与腐蚀时间呈线性关系;大理石细骨料比大理石粗骨料更有利于减小腐蚀深度。     

机制砂与天然细砂混掺配制高性能混凝土耐久性的研究

研究了机制砂与天然细砂混掺配制的混凝土与中砂混凝土的抗压强度、抗冻性、抗渗性、抗硫酸盐侵蚀与抗碳化性能。试验结果表明:机制砂与水泥浆体界面的结合良好;机制砂中的石粉填充了混凝土中的孔隙,提高了混凝土的密实性;机制砂与天然细砂混掺配制的混凝土,其抗冻性、抗渗性、抗硫酸盐侵蚀及抗碳化性能都优于中砂混凝土。     

浒泊机制砂与河砂混凝土力学性能的对比研究

针对山西存在的严重缺砂问题，对太谷浒泊人工机制砂与河砂混凝土的力学性能进行了对比研究，研究表明，太谷浒泊人工机制砂在C30及以下的混凝土中应用是可行的。     

高强混凝土脆性及其改善措施研究

研究了采用普通骨料和机制砂配制的 C60和 C80高强混凝土的脆性特征及其改善措施。结果表明,混凝土中掺加活性掺合料和纤维都能够提高混凝土的抗裂性能;钢纤维与聚丙烯纤维混合掺入混凝土中,其增韧效果明显优于单独使用;随着混凝土强度提高,混凝土脆性变大,同种增韧材料的增韧效果有下降的趋势。     

Effect of the treatment of wood shavings on the physico-mechanical characteristics of wood sand concretes

This study investigates the effect of a wood shaving treatment on the physico-mechanical characteristics of wood sand concretes. The two main objectives of this work are to improve a lightweight sand concrete and to valorise local materials and industrial wastes. Three wood shaving contents, two types of sand concretes (dune and river sand concrete) and a preliminary wood shaving treatment have been used. Sand, cement, filler, admixture and water composed the sand concrete matrix. The shaving treatment appreciably increases the mechanical strength of the studied composites without a large influence on thermal conductivity. The shrinkage of the composite is considerably reduced and the wood–matrix adherence is improved. At low wood contents, the dune sand concrete remains always slightly more insulating and less strong than the river sand concrete. At higher wood contents, the two concretes present almost similar properties.     

Mechanical and durability properties of concrete made with dredged marine sand

The process of depletion of sources of natural aggregates challenges the production of technically and environmentally adequate concrete. Alternative material from marine sources, especially for concrete maritime structures, could represent an acceptable solution for this problem and it might also be of great interest for port management. This research work describes the study of the mechanical and durability properties of concretes fabricated with dredged marine sand (DMS) as a fine granular corrector in partial substitution of raw sand (from 15% to up to 50% by raw sand mass) designed for harbor pavements. Three DMS samples were extracted from the Port of Barcelona. The material was stockpiled in the open air and no washing, drying or decontamination process was carried out. Mineralogical, physical and chemical properties of DMS material were determined. Eight different mixtures were produced incorporating three types of DMS material as granular corrector in partial substitution of crushed limestone raw sand. The concretes were submitted to compressive strength tests after 7 and 28 days of moist curing, as well as density, absorption, accessible pores, elastic modulus, tensile and splitting tensile strength, abrasion, capillary suction, water penetration under pressure and ultrasonic pulse velocity (UPV) tests, all of them after 28 days of moist curing. This study shows that dredged marine sand can be successfully used as a fine aggregate for concrete production. This is justified by the similar physical and mechanical properties of concrete made with DMS comparing to reference concrete. It was verified that the use of DMS in substitution of raw sand maintained or reduced the accessible pores, the sorptivity and the water penetration depth under pressure.     

Durability of concrete pipes subjected to combined steam and carbonation curing

A beneficial use of carbonation as an auxiliary curing regime for concrete pipes was studied in an attempt to reduce steam curing time, improve durability performance and explore the possibility of using concrete pipe to sequester carbon dioxide. Durability performance of the carbonated concretes was characterized by carbon uptake, strength gain, pH, calcium hydroxide content, permeability, sorptivity and sulfate and acid resistance. It was found that initial curing using steam is necessary to facilitate carbonation. Although the contribution of early carbonation to strength gain is not noticeable after initial steam curing, the process is unique in promoting enhanced durability performance of concrete. The early carbonation leads to a reduction in calcium hydroxide near the surface while maintaining a pH above the corrosion threshold value at the core. Carbonated concretes also exhibit improved resistance to sulfate attack, water absorption, and chloride ion penetration. A carbon uptake of 9% by cement mass makes concrete pipe an ideal candidate for carbon dioxide capture and storage.