混凝土外加剂有关问题的探讨.doc

混凝土外加剂有关问题的探讨 作者： 日期：17 个人收集整理 勿做商业用途混凝土外加剂有关问题的探讨摘要:在水泥混凝土中掺加外加剂可以体现出良好的性能,所以外加剂在水泥混凝土中被广泛采用,但也存在一些问题.本文阐述了水泥混凝土中掺加外加剂的分类及性能与一些常易出现的问题,提出了一些改善措施。 关键词:外加剂；性能;分类；坍落度；水泥 掺加混凝土外加剂可以体现出良好的性能，所以混凝土外加剂已经成为制备混凝土的一种重要组分,随着混凝土外加剂的广泛应用,也使混凝土材料的发展实现了质的飞跃。在国内,高标号混凝土几乎全部掺加外加剂. 工程中所用水泥品种很多，外加剂的品种也很多,在工程使用中容易存在这样一些问题.例如某试验室在配制坍落度为90mm120mm的C30混凝土时，外加剂采用成都市锦江区茂华建材厂的外加剂,水泥来源于四川万源大巴山水泥厂,掺加1。2的外加剂用量，减水率仅为9。5%,减水率达不到技术指标;而后采用万州科华水泥进行实验，在外加剂品种不变,掺量为0.8的时候,减水率达到了18。2，这是使用同种外加剂与不同水泥品种的问题;该试验室在配制坍落度为180mm220mm的C30的水下桩混凝土时，水泥为华新水泥，外加剂分别采用成都市锦江区茂华建材厂的外加剂与重庆海木交通技术有限公司的外加剂,在相同外加剂的掺量情况下，减水效果有很大的不同.所以，不同品种水泥掺配相同的外加剂与相同品种的水泥掺配不同的的外加剂表现出不同的效果是本文重点探讨的问题。 一、混凝土外加剂的分类 外加剂种类很多，功能多样，所以在国内与国外分法是不一致的,常有以下三种分类方法. （1）按其主要功能可以分为四类。 1）改善混凝土拌和物流变性能的外加剂，包括各种减水剂、引气剂和泵送剂等。 2）调节混凝土凝结时间，硬化性能的外加剂，包括缓凝剂、早强剂和速凝剂等。 3)改善混凝土耐久性的外加剂,包括引气剂、防水剂和阻锈剂等. 4)改善混凝土其他性能的外加剂,包括加气剂、膨胀剂、着色剂、防水剂和泵送剂等. (2）混凝土外加剂按化学成分分为有机外加剂、无色外加剂和有机无机复合外加剂。 （3)混凝土外加剂按使用效果分为减水剂、调凝剂（缓凝剂,早强剂,速凝剂）、引气剂、加气剂、防水剂、阻锈剂、膨胀剂、防冻剂、着色剂、泵送剂以及复合外加剂(早强减水剂,缓凝减水剂，缓凝高效减水剂)。 二、常用混凝土外加剂 1。减水剂 混凝土减水剂是指在保持混凝土坍落度基本相同的条件下,具有减水增强作用的外加剂。 （1）混凝土掺入减水剂可以达到比较理想的效果。 1)保持坍落度不变，掺减水剂可降低单位混凝土用水量5%25%，提高混凝土早期强度，同时改善混凝土的密实度，提高耐久性。 2）保持用水量不变，掺减水剂可增大混凝土坍落度10mm20mm，能满足泵送混凝土的施工要求。 3）保持强度不变，掺减水剂可节约水泥用量5%20%. (2）减水剂常用品种有普通型减水剂和高效减水剂. 1)普通型减水剂木质素磺酸盐类,如木质素磺酸钙(简木钙粉，M型)，适宜掺量为水泥用量的0。20。3,在保持坍落度不变时,减水率为1015。在相同强度和流动性要求下,节约水泥10左右。 2)高效减水剂,如NNO减水剂，掺入NNO的混凝土之后就具有耐久性、搞硫酸盐、抗渗、抗钢筋绣蚀等均优于一般混凝土的特点。高效减水剂适宜掺入量为水泥质量的1%左右，在保持坍落度不变时,减水率为1418%。一般3d可提高混凝土强度60,28d可提高30%左右.在保持相同混凝土强度和流动性要求下,可节约水泥15左右。 2.早强剂 混凝土早强剂是指能提高混凝土早期强度,并对后期强度无显著影响的外加剂,若外加剂兼有早强和减水作用则称为早强减水剂. 早强剂多用于抢修工程和冬季施工的混凝土.目前常用的早强剂有：氯盐，硫酸盐,三乙醇胺和以它们为基础的复合早强剂。 (1）氯盐早强剂。常用的有氯化钙和氯化钠.氯化钙能与水泥中矿物成分C3A或水化物Ca（OH）2反应，其生成物增加了水泥石中固相比例，有助于水泥石结构形成，还能使混凝土中游离水减少,孔隙率降低,因而掺入氯化钙能缩短水泥的凝结时间,提高混凝土强度、密实度和抗冻性。但氯盐掺量不得过多,否则会引起钢筋锈蚀. （2）硫酸盐早强剂.常用的有硫酸钠早强剂,又称元明粉，是一种白色粉状物,易溶于水,掺入混凝土后能与水泥水化生成的氢氧化钙作用，生成的CaSO4均匀分布在混凝土中，并 与C3A反应，迅速生成水化硫铝酸盐,加快水泥硬化。 （3)三乙醇胺早强剂。是一有机化学物质,强碱性,无毒,不易燃烧,溶于水和乙醇,对钢筋无锈蚀作用。单独使用三乙醇胺,早强效果不明显，若与其他盐类组成复合早强剂，早强效果则比较明显。三乙醇胺复合早强剂是由三乙醇胺、氯化钠、亚硝酸钠和二水石膏等复合而成。 3.引气剂 引气剂是在混凝土搅拌过程中，能引入大量分布均匀的稳定而密封的微小气泡，以减少拌和物泌水和离析,改善和易性,同时显著提高硬化混凝土抗冻融耐久的外加剂,兼有引气剂和减水作用的外加剂称为引气减水剂。引气剂主要有松香树脂类，如:松香热聚物，松脂皂;有烷基苯磺酸盐,烷基苯酚聚乙烯醚等。引气剂有时也采用脂肪醇磺酸盐类以及蛋白质盐。其中,以松香树脂类的松香热聚物的效果较好,最常使用。 引气减水剂减水效果明显,减水率较大,不仅具有引气作用，还能提高混凝土强度,弥补由于含气量而使混凝土强度降低的不利,而且节约水泥.基于上述优点引气减水剂常用于道路、桥梁、港口和大坝等工程上。要解决混凝土遭受冰冻,海水侵蚀等作用时的耐久性问题，可采用的引气减水剂有改性木质素磺酸盐类,烷基芳香磺酸盐尖以及由各类引气剂与减水剂组成的复合剂。引气剂和引气减水剂,除用于抗冻、防渗、抗硫酸盐混凝土外，还宜用于泌水严重的混凝土,素混凝土以及对饰面有要求的混凝土和轻骨,不宜用于蒸养混凝土和预应力混凝土。无论在哪种混凝土中,掺引气剂或引气减水剂，其掺量都十分微小，一般为水泥用的0.5/100001.5/10000。 4.缓凝剂 缓凝剂是指延缓混凝土凝结时间,并不显著降低混凝土或长距离运输的混凝土。缓凝剂有糖类，如糖钙；有木质素磺酸盐类,如木质素磺酸钙，木质素磺酸钠羟基酸以及盐类和无机盐类;还有胺盐及衍生物，纤维素醚等。最常用的是糖蜜和木质素磺酸钙，糖蜜的效果最好。 5.泵送剂 泵送剂是指能改善混凝土拌和物的泵送性能,使混凝土能顺利通过输送管道,不阻塞,不离析,粘塑性良好的外加剂。其组分包含缓凝及减水组分，增稠组分（保水剂）,引气组分，高比表面无机掺合料。应用泵送剂温度不宜高于35摄氏度，掺泵送剂过量可能造成堵泵现象。泵送混凝土水灰比为0。450。60，砂率宜为38%45%。最小水泥用量应大于0。3t/m3。 混凝土中掺用外加剂前，必须了解不同外加剂的性能，相应的使用条件,查阅出厂产品说明书。否则使用不当就会酿成事故,例如剂量过大和拌合不匀,此外还应注意下面几种情况. （1)外加剂的使用应严格执行现行技术规范,外加剂的质量应符合现行国家标准的要求。 (2）外加剂的品种、掺量必须根据混凝土性能要求,施工和气候条件,混凝土采用的原材料和配合比等因素,通过试验，调整后进行确定。掺用含氯盐的外加剂,要特别注意对钢筋锈蚀和对混凝土的腐蚀。 （3）蒸汽养护的混凝土和预应力混凝土，不宜掺用引气剂和引气减水剂。 三、掺混凝土外加剂常出现的问题 (1）使用相同的外加剂与不同品种的水泥掺配，效果不同。 (2）使用相同的水泥与不同品种的外加剂掺配,效果不同。 效果不同具体表现在以下几个方面。 1)流动性：如同品种水泥掺不同外加剂与同品种外加剂掺不同水泥，减水率各不相同,以致于坍落度各不相同. 2)粘聚性:如同品种水泥掺不同外加剂与同品种外加剂掺不同水泥，粘聚性各不相同。 3）保水性：如同品种水泥掺不同外加剂与同品种外加剂掺不同水泥,保水性各不相同。 四、掺混凝土外加剂常出现的问题的原因分析 为什么会出现相同外加剂与不同品种的水泥掺配，相同水泥与不同品种外加剂掺配会出现上面那些问题，笔者通过分析认为主要原因是外加剂与水泥不相适应,那么什么叫水泥与外加剂的适应性?我们可以这样定义：将经检验符合技术标准要求的外加剂与同样经检验符合技术标准的水泥所配制的混凝土配合使用,如能产生应有的效果，就认为这种水泥与这种外加剂是适应的;相反,如不能产生应有的效果则认为这种水泥与这种外加剂是不相适应的。现在就从以下几个方面来分析水泥与外加剂的适应性问题。 （1)水泥中石膏的影响.现在有些水泥厂为节省生产成本，采用硬石膏或工业副产品石膏(无水石膏）代替二水石膏作为水泥调凝剂,在进行水泥检验时，不论采用哪种石膏生产的水泥区别都不大，但是掺加减水剂时,却表现出不同的效果，特别是用无水石膏作为调凝剂的水泥遇到木钙和糖钙减水剂时,就会产生严重的不相适应性，既得不到预期的减水效果,还会引起流动性损失过快甚至异常的凝结。其原因就是石膏结晶形态不同，对木钙或糖钙减水剂的吸附能力也不相同。 （2)水泥中碱含量的影响。水泥与外加剂是否相适，水泥中碱的含量会对其产生很大的影响，主要表现在对减水剂的塑化效果的影响，水泥中碱含量增大不但会造成减水剂的塑化效果变差,而且还会导致坍落度损失和凝结时间缩短.需要注意的是真正影响减水剂作用效果的碱是可溶性碱，由于水泥品种不同,虽然碱含量相同，但是可溶性碱的含量并不相同,所以我们不能这样认为水泥碱含量较高的水泥与外加剂的适应性就一定不好。 （3）水泥中矿物成分和石膏掺量的影响。如水泥与外加剂出现不适应也可能是水泥中的C3A含量太高,或石膏与C3A的比例太小的原因所致. （4)水泥细度的影响。因为现在有些水泥厂盲目追求水泥的早期强度,采用提高水泥的粉磨细度,为了达到较好的塑化效果就只能增加减水剂的掺量。这是因为水泥颗越细，水泥的比表面积越大，那么对减水剂分子的吸附量就越大。 (5)水泥的新鲜度和水泥的温度的影响。因为新鲜的水泥的正电性比较强,所以对减水剂的吸附能力比较大，所以水泥越新鲜，减水剂对水泥的塑化效果可能要差一些；还有水泥的温度越高,减水剂对水泥的塑化效果也差一些，坍落度的损失也较快一些。 五、改善措施 (1）水泥生产厂要注意尽量不用硬水石膏作为调凝剂. （2）施工方如遇到水泥为掺硬水石膏时,要采用不含木钙或糖钙的外加剂. （3)施工方在施工前应把外加剂与水泥送到试验室进行适应性试验. （4)施工方在水泥每批次进入施工现场后,要把新进的水泥与外加剂送到试验室再做适应性试验。 六、结束语 在混凝土中掺加外加剂体现出很多好的作用，目前所遇到的主要问题是外加剂与水泥的适应性问题。这需要我们在生产实践中重视存在的问题，并采取一些措施和有效的技术手段，努力将水泥与外加剂不相适应造成的工程质量问题降到最低程度。 。 Discussion of issues related to concrete admixturesAbstract： In mixing cement concrete admixtures can demonstrate good performance, so the admixtures in the concrete is widely used， but there are some problems. This paper describes the mixing of cement concrete admixtures and performance with a number of classification problems are often easy to put forward a number of improvement measures。Keywords: additive; performance; classification; slump; cementAdmixture of concrete admixtures can demonstrate good performance， so the preparation of concrete, concrete admixtures has become an important component， along with the extensive application of concrete admixtures， but also to the development of concrete materials to achieve a qualitative leap。 In China， almost all highgrade concrete admixture admixtures.Project in many kinds of cement, admixtures of many varieties， easy to use in the project there are such problems. For example, a laboratory in the preparation of the slump of 90mm 120mm C30 concrete, admixtures used building materials plant in Chengdu Jinjiang Maohua admixtures， cement from the Daba Mountains in Sichuan Wanyuan cement, admixture 1。2 plus dosage， water reduction rate was only 9.5 water reduction rate of less technical indicators； Wanzhou Kehua cement and then used for experiments in the same admixture species, dosage of 0。8% of the time, reducing the water rate reached 18.2 ， which is the same kind of cement admixtures and different varieties of the problem； the laboratory slump in preparation for the 180mm 220mm of C30 concrete underwater piles, cement Huaxin Cement, additives were used to Chengdu Jinjiang District Maohua building materials plant in Chongqing， the sea timber traffic admixture with admixtures Technology Co。， Ltd。， in the case of the same admixture content， waterreducing effects are very different. Therefore, the different varieties of the same cement mixed with additives mixed with the same species with different cement admixtures showed different results in this article focus on the problem。First， the classification of concrete admixturesMany different types of additives， functional diversity， so in the domestic and foreign sublaw is inconsistent， often following three classification methods.(1) can be divided into four categories according to their main function.1) to improve the rheological properties of the concrete mixing additives， including water reducer， air entraining agent and pumping agent。2） adjust the setting time of concrete hardening properties of admixtures， including retarder, early strength agent, and quick-setting agent。3） to improve the durability of concrete admixtures including air entraining agents， water repellent and rust agent。4) to improve other properties of concrete admixtures， including the filling agent， expanding agent, coloring agent, water repellent and pumping agent.（2) The concrete admixture additive according to the chemical composition is divided into organic， inorganic and organic additives colorless compound additives.(3) into effect by the use of concrete superplasticizer admixture， condensate transfer agent （retarders， early strength agent, accelerator）， air-entraining agents, filling agents， waterproofing agents， rust agent, expansion agent, antifreeze, colorants， pumping agent and composite additives （early strength superplasticizer， retarding superplasticizer, retarding superplasticizer).Second， commonly used in concrete admixtures1 water-reducing agentConcrete waterreducing agent is essential in maintaining the slump of concrete under the same conditions， with the enhancement of waterreducing admixtures.(1） concrete mixed with water reducer can achieve more satisfactory results。1） to maintain the same slump， concrete mixed with water-reducing agent can reduce the unit water consumption of 5 to 25%, improve the early strength of concrete， while improving the density of concrete to improve durability。2） to maintain the same amount of water, mixed water-reducing agent may increase the slump of concrete 10mm 20mm， concrete construction to meet the pumping requirements.3) maintain the same intensity, the amount of cement mixed with water-reducing agent can save 5 to 20%.（2) water-reducing agent commonly used varieties of ordinary waterreducing agent and superplasticizer。1） Ordinary type superplasticizer lignin sulfonate, such as calcium lignosulfonate (simple wooden calcium, Mtype)， cement content for the appropriate amount of 0。2% to 0。3, while maintaining the same slump When water reduction rate of 10 to 15。 In the same strength and liquidity requirements, the savings of about 10 of cement.2） superplasticizer, such as NNO superplasticizer, after incorporation of NNO concrete durability, engage sulfate， impervious， corrosion resistant stainless steel characteristics were better than normal concrete. Superplasticizer suitable for the incorporation of about 1 of cement quality, while maintaining the same slump， the reduced water rate of 14% to 18%. 3d can improve the general strength of concrete 60%， 28d can be increased by 30 percent。 Maintaining the same concrete strength and liquidity requirements， it can save about 15% of cement。（2） early strength agentConcrete early strength agent is able to improve the early strength of concrete, and the late strength had no significant effect of admixture, if both the earlystrength admixture and water-reducing effect is referred to as early strong reducing agent。Early strength agent used for repair work and construction of concrete in winter. Early strength agent currently used are: chloride, sulfate， triethanolamine, and the compound based upon them early strength agent.（1) chlorideearlystrength agent. Calcium chloride and sodium chloride are used。 Calcium chloride with the C3A cement minerals or hydrates Ca （OH) 2 reaction， the resultant increase in the proportion of solid phase of cement to help cement structure formation, but also to reduce the free water in the concrete， porous rate decreased, and thus cement mixed with calcium chloride to reduce the setting time and improve the concrete strength, density and frost resistance. However, chloride dosage shall not be excessive, otherwise it will cause steel corrosion.（2) sulfateearly-strength agent。 Commonly used sodium sulfate early strength agent, also known as sodium sulfate， is a white powder， soluble in water， mixed with concrete and cement hydration can be generated after the effect of calcium hydroxide， resulting in uniform distribution of CaSO4 concrete and react with C3A， hydration sulphoaluminate quickly generate, accelerate the cement hardening.(3) triethanolamine early strength agent。 Is an organic material, highly alkaline, non-toxic， nonflammable, soluble in water and ethanol， no corrosion of steel role. Triethanolamine alone， early strength is not obvious, if the compound with other salts formed early strength agent, early strength effect is more obvious。 Triethanolamine complex early strength agent is triethanolamine, sodium chloride, sodium nitrite and other gypsum composite。3 air-entraining agentAirentraining agent in the concrete mixing process, introduce a large number of stable and uniform distribution of tiny air bubbles sealed in order to reduce bleeding and segregation mixture to improve workability， while significantly increasing resistance to freezethaw durability of hardened concrete admixtures， both airentraining agent and waterreducing effect of air-entraining admixtures called water-reducing agent。 Airentraining agents are rosin resin， such as： hot rosin polymer， resin soap; have alkylbenzene sulfonates, alkyl phenol polyethylene ether. Air-entraining agent is sometimes used alcohol sulfonate salt and protein。 Among them， rosin resin， rosin hot polymer class is better， the most commonly used.Air-entraining water-reducing effect of significantly reducing agent, water rates, not only in air with a lead role, but also improve the strength of concrete， make up for lower strength of concrete containing gas leaving the negative, and save cement. Based on the above advantages of air-entraining water-reducing agent commonly used in roads， bridges, ports and dams and other projects. To solve concrete subjected to freezing， the role of sea erosion durability problem， the airentraining waterreducing agent can be used with modified lignin sulfonate, alkyl aromatic sulfonates from the tip and cut all kinds of air-entraining agents and agent consisting of combinations. Airentraining agent and air-entraining waterreducing agent, in addition to antifreeze, impermeable, concrete sulfate resistance， but also appropriate for serious bleeding of concrete， plain concrete and the concrete finishes are required and light bone, not for steamcured concrete and prestressed concrete。 In either concrete, mixed with air entraining agent or airentraining waterreducing agent, the dosage is very small, usually cement used 0。5/10000 1。5/10000.4 retarderRetarder is delaying the setting time of concrete is not significantly reduce longdistance transport of concrete or concrete。 Retarders are carbohydrates such as sugar， calcium； a lignin sulfonate, such as calcium lignosulfonate, lignin sulfonate salts and hydroxy acids and inorganic salts; also amine salts and derivatives， fiber ether and other factors。 The most commonly used is molasses and calcium lignosulfonate， molasses is the best。5 pumping agentPumping agent is able to improve the pumping performance of concrete mixture， so smoothly through the concrete pipes， nonblocking, not isolation， viscoplastic good admixture。 Its components and the reduction in water containing retarding component， thickening fraction (insurance agent）, airentraining component, high surface area inorganic admixture。 Temperature is not higher than the pumping agent application 35 degrees Celsius, mixed with pumping the pump blocking agent overdos