有机膦酸类化合物在混凝土工程中的应用及缓凝机理研究进展

Research Progress on Application of Organic Phosphonic Acid Compounds in Concrete Engineering and Their Retarding Mechanism

通过掺加具有水化热抑制作用的外加剂来降低胶凝体系的水化放热量及放热速率是减少混凝土中温度裂缝的重要措施。相对于葡萄糖酸钠和糖钠等常用缓凝材料,有机膦酸类化合物对硅酸盐水泥具有更为有效的水化热抑制作用和缓凝作用。过去几十年,有机膦酸类化合物在国外常被作为缓凝材料应用于工民建、油田固井和一些有特殊要求的混凝土工程中。在我国,有机膦酸类化合物主要应用在油田固井混凝土工程中,近年来在越来越多的工民建混凝土工程中也有所应用,但是其应用范围仍然十分有限。有机膦酸类化合物具有以下特征:(1)在一定掺量范围内可大幅降低硅酸盐水泥的水化放热速率和放热量,改善硅酸盐水泥水化放热过程;(2)有机膦酸类化合物对水泥熟料含量的变化不敏感,与硅酸盐水泥、聚羧酸减水剂和萘系减水剂均具有较好的适应性;(3)在一定掺量范围内,有机膦酸类化合物可改善混凝土拌合物性能,提高混凝土长期力学性能;(4)有机膦酸类化合物的主链结构具有高温稳定性,适用温度达200℃以上,在高温环境下其对硅酸盐水泥仍具有较强的缓凝作用。有机膦酸类化合物对硅酸盐水泥水化的影响较复杂,目前硅酸盐水泥缓凝机理尚不十分明确。不同学者对此持有不同的观点。其中一种观点认为:有机膦酸类化合物首先促进水泥中Ca^2+溶解,在富铝层表面促进水泥矿物水化,进而促进铝酸三钙(C3A)的水化;接着与水泥中Ca^2+结合,在硅酸三钙(C3S)表面形成半透水的稳定螯合物,抑制C 3S的水化,从而抑制水泥的进一步水化。而另一种观点认为:有机膦酸类化合物有效抑制了钙矾石凝胶向晶体转变的成核和生长过程,并认为延缓钙矾石晶体的生长是导致硅酸盐水泥缓凝的主要原因。本文从有机膦酸类化合物在混凝土工程中的应用着手,总结了有机膦酸类化合物对硅酸盐水泥水化动力学的影响以及缓凝机理的研究进展。基于此,为进一步扩大有机膦酸类化合物在混凝土工程中的应用范围,提出了应进一步研究有机膦酸化合物对混凝土力学性能、体积稳定性、热力学性能和耐久性能的影响,同时应进一步研究有机膦酸类化合物对硅酸盐水泥水化动力学的影响及缓凝机理。

Reducing the cumulative hydration heat and heat evolution rate of the cementitious system by the means of adding an admixture with hydration heat inhibition is an important measure to reduce the temperature cracks in the concrete.Organic phosphonic acid compounds have more effective hydration heat inhibition and retardation effects on Portland cement.In the past few decades,organic phosphonic acid has been widely used in industrial and civil construction engineering,oil field cementing engineering and some concrete projects with special requirements.The application of organic phosphonic acid compounds in China is mainly concentrated in oilfield cementing concrete engineering.In recent years,it has also been more and more popular applied in civil engineering concrete projects,but the scope and extent of application are still very limited.In summary,organic phosphonic acid compounds have the following characteristics:(1)they can greatly reduce the cumulative hydration heat and heat evolution rate within a certain dosage.(2)They aren t sensitive to changes in cement clinker content,and they have good adaptability with Portland cement,polycarboxylate water reducer and naphthalene water reducer.(3)They can improve the performance of concrete mix and improve the long-term mechanical properties of concrete at a certain dosage ranges.(4)The main chain structure of organic phosphonic acid compounds have high temperature stability,and the applicable temperature is above 200℃.They can maintain strong retarding effect on Portland cement at a higher temperature.The effect of organic phosphonic acid compounds on the hydration of Portland cement is complicated,and the mechanism of retardation of Portland cement is not very clear.Different scholars hold different views on this.One of the views proposes that it firstly promotes the dissolution of Ca^2+in the cement,promotes the hydration of the cement mineral on the surface of the aluminum-rich layer,and promotes the hydration of the tricalcium aluminate(C3A).Then,they form a semi-permeable stable chelate on the surface of tricalcium silicate(C3S)in combination with Ca^2+,which inhibits the hydration of C 3S and inhibits further hydration of cement.Another point of view proposes that the organophosphonic acid compound effectively inhibits the nucleation and growth process of ettringite gel to crystal transformation,and it believes that delaying the growth of ettringite crystals is the main cause of retardation of Portland cement.In this paper,the application of organic phosphonic acid compounds in concrete engineering is summarized.The study progress of organic phosphonic acid compounds on hydration kinetics and retardation mechanisms of Portland cement are also summarized.Based on this,in order to further expand the application range of organic phosphonic acid compounds in concrete engineering,it is proposed to further study the effects of organic phosphonic acid compounds on the mechanical properties,volume stability,thermodynamic properties and durability of concrete.And the effect of organic phosphonic acid compounds on hydration kinetics of Portland cement and its retardation mechanism are further studied.