Tons of sulfur concrete
March 13, 2014
Published in corporate Gazprom Magazine Issue 1–2
Gazprom entering construction material market
The importance and economic efficiency of innovations consistently increase when their application provides for solving several tasks at a time. This can be exemplified by Gazprom’s project for developing and initiating the production of modified sulfur binder as well as its materials and structures. This project will permit Gazprom to overcome production obstacles related to gas production from high-sulfur gas fields and to simultaneously create and develop a new promising sub-industry in Russia oriented at production of construction materials.
Sulfur in roads
Alexey Miller, Chairman of the Gazprom Management Committee explained the comprehensive effect of the Company’s new innovative project at the Russian State Council Presidium meeting on economic modernization and innovative development on May 17, 2013. He made it clear that “the main constraint for production growth at the Astrakhan and Orenburg fields is a substantial amount of sulfur evolving from gas in conditions of low demand for sulfur both in the international and the domestic markets. Our institutes have developed sulfur-enhanced asphalt modification technologies making it possible to increase asphalt strength and ductility, extend the time between road repairs to 5–7 years with a considerable economic effect for road construction… we believe, this technology could produce a triple effect. Firstly, it would help to reduce the environmental load in Astrakhan and Orenburg, where great amounts of sulfur are accumulated. Secondly, it would increase the economic efficiency of gas production in those fields. And, thirdly, it would considerably improve the road performance, especially in the regions with huge temperature swings, as well as cut down the road construction costs”.
The method of modifying bitumen with sulfur is not new in itself, it had been used in the industry for the first time as long as 100 years ago, but large-scale activities in this area both in Russia and abroad were initiated only in 1970s. In 1986 the Guidelines for Use of Sulfur in Hot Mix Asphalt were published in the USSR. Due to well-known events, further development of these projects in Russia came to a standstill then and they were not put into practice, but Gazprom picked up the baton. In 1998 Gazprom VNIIGAZ started investigating the possibilities of using sulfur in road construction and in October – December 2002 sulfur asphalt concrete was laid for the first time when repairing the road surface of the bridge in Krylatskoye. The work was carried out under extreme conditions (rain, snow, subzero temperatures), and its final stage – at the temperature below minus 20 degrees, when laying ordinary asphalt concrete would be impossible in practice. In June 2010 sulfur asphalt concrete was laid on the 50–51 kilometer area of the Moscow Ring Road, which required 558 tons of the material. The road area successfully endured even extreme summer heat. Thus, the experience has proved the qualitative superiority of the sulfur asphalt mixture, which is produced by adding modified sulfur binder into bitumen prior to traditional road surface laying.
At present, the advantage of using modified sulfur binder in road construction is practically assured, and it is not incidental that at the abovementioned meeting Dmitry Medvedev, Prime Minister of the Russian Federation tasked the Ministry of Transport to investigate with Gazprom the issue of implementing a number of pilot projects for constructing sulfur asphalt concrete roads in regions with different temperature conditions.
At the same time, it should be noted that despite all the advantages of sulfur asphalt concrete, even its commercial output doesn’t solve Gazprom’s key problem – excessive production of sulfur at the Astrakhan and Orenburg fields. The volumes of sulfur surplus, in other words, the sulfur that can’t be sold, reach 2 to 3 million tons a year, and in case of production growth at both fields this figure will be even higher. And even if all the asphalt concrete produced in Russia is mixed with modified sulfur binder, its production will demand only from 100 to 200 thousand tons of sulfur annually. It is explained by the fact that the sulfur content in sulfur asphalt concrete is very low. According to the research, the 40 per cent sulfur content is the upper limit of its positive influence on the sulfur bitumen binder (the usual content being from 10 to 30 per cent). Moreover, the content of such binder in the asphalt concrete mix accounts for a maximum of seven per cent (usually being five to six per cent).
Considering this fact, in parallel with sulfur asphalt concrete production, Gazprom is planning to produce sulfur concrete for construction purposes within the integrated Program for setting up and developing a sub-industry to produce construction and road construction materials based on modified sulfur binder. Gazprom Sera, Gazprom’s operator responsible for marketing this type of products is the Program developer and contractor. The Program is also aimed at achieving a comprehensive effect providing for the solution of purely intra-group tasks as well as a plenty of problems of the Russian construction industry.
Such prospects are due to the specific mechanisms of sulfur concrete production and application. As already stated, the content of the 16th chemical element in the sulfur asphalt mix is not high. Sulfur concrete is a different story, though. Here sulfur is the basic structure-forming material, the main binder extender replacing neat cement. Its content in the binding material exceeds 90 per cent. Today some 60 million tons of cement is produced in Russia. If sulfur-based construction materials manage to cover at least ten per cent of the market, over five million tons of this element will be involved in production, thus making it possible to fully solve the existing problem of sulfur surplus and increase gas production at high-sulfur fields, including those not owned by Gazprom.
For the Russian construction industry the advantages are also obvious. Not only will the sulfur concrete application make it possible to boost the production volume of construction materials under the conditions of ever-increasing demand, it will also substantially improve the reliability of facilities made of it. The main advantages of sulfur concrete as compared to conventional concrete include fast gain of strength, its retention and better strength properties (bearing and flexing strength), the ability of this material to endure tension, high chemical (corrosion) resistance, high tolerance to acid and saline media as well cold resistance several times exceeding that of the conventional concrete. Such characteristics as low thermal conductivity and low water absorption capacity, solidification in freezing weather, recyclability, minor shrinkage and good adhesion (bonding effect between the surfaces of dissimilar materials) should also be mentioned. Here, similar to sulfur asphalt we see that sulfur concrete gives a head start to Portland cement (hereafter referred to as cement) with regard to the durability of installations made of it, as well as to performing the construction activities. Conventional concrete can’t be laid in freezing weather (or it should be heated up first), whereas sulfur concrete hardens at any temperature between plus 40 and minus 40 degrees.
The properties of sulfur concrete are explained by its inner structure, which was closely studied by North American scientists. Sulfur with no admixture is a homogeneous substance, which means that its molecules are closely arranged. The presence of a filling agent makes sulfur molecules ‘fasten’ the filling agent molecules and fill the inner cavities of the resulted substance so that porosity becomes almost invisible (even to a microscope).
Low porosity of sulfur concrete largely determined its spheres of application. It concerns sulfur concrete use as the main construction material for waste storages, waste water sewers, refiners, piles, pipes, sewage collectors, different prefabricated structures, that is to say, all underground utility networks, as well as offshore structures and dams. Sulfur concrete may also be of interest for the gas industry, as it is a perfect material for constructing pipeline wrap-around concrete weights, road slabs and piles used as a part of the gas field infrastructure, etc.
It should be mentioned that sulfur concrete is convenient to produce. Anyone who has ever made mortar knows that it consists of three components: cement, sand and water. Water is not required for preparation of sulfur concrete and almost any type of sand may be used. The fineness of sand should be 2.4 for cement, whereas for sulfur concrete this parameter may be less than 1. In other words, dust sands, or blown sands will suffice for sulfur concrete, while conventional concrete would come apart if they were used. It turns out that high-quality constructions or structures can be made using local materials.
Astrakhan waiting for pilot production facility
However, it should be pointed out that the properties of sulfur concrete are more dependent on complying with the production process and controlling the quality of raw materials at all the production stages, than the properties of cement concrete. Today sulfur-based construction materials in Russia are manufactured by small companies mostly in backyard conditions. Such companies can easily cast a slur on sulfur-based materials. Such an amateur approach and the absence of precision equipment capable of adjusting the heating of the mixture within the range of plus-minus one degree, may result in sulfur concretes (on achieving the temperature of 150 degrees) emitting hydrogen sulfide and sulfur dioxide – neuroparalytic gases dangerous for people. That is why establishing production facilities capable of delivering large quantities of sulfur concrete in strict compliance with process standards is especially important today.
That is exactly the course followed by Gazprom Sera today. At the first stage the functional pilot production facility has to be set up to serve as the ground for developing and producing modified sulfur binders, as well as sulfur concrete and sulfur asphalt mixes, testing technologies for sulfur-based materials and structures production, designing and commercial trials of structures, materials, machines and equipment. At present, the company employees are performing R&D and generating regulatory documents concerning the manufacture of new products. It is also planned to train specialists to be engaged in creating materials and structures from sulfur. In fact, it will be a R&D and training center, a testing ground and a production company all in one. According to Marat Garayev, Deputy Head of Gazprom’s Gas and Liquid Hydrocarbons Marketing and Processing Department, Director General of Gazprom Sera, “It is planned to fit the pilot production facility with the state-of-the-art equipment based on eco-friendly unmanned technologies. Granulated modified sulfur cements (currently the product developers estimate the possible annual output at some 120 thousand tons a year with the possibility of further growth), sulfur concrete and sulfur asphalt mixes, road slabs for surfacing temporary and permanent roads, square piles with untensioned reinforcement, gas pipeline wrap-around concrete weights will be the main types of delivered and sold products. All the structures will be manufactured in strict compliance with the GOST standard.”
By now, Gazprom Sera specialists jointly with the LENNIIGIPROKHIM Institute have prepared a feasibility study, an investment rationale and basic engineering solutions for each of the production units. A bidding procedure for choosing the company designer will be organized in the nearest future. Design operations completion and construction start are due this year, and the plant commissioning is scheduled for 2016. It is to be located in Astrakhan; later on such plants will also appear in Orenburg.
It will be the next stage of the program – developing the network of sulfur-containing materials & products manufacturers, which will require government support. The most efficient kind of assistance from the government authorities would be inclusion of the project for the use of sulfur in the national economy into the federal target program. It will allow the program participants to obtain credits on favorable terms, while acknowledging sulfur-containing materials as innovative will provide tax breaks for their producers. This issue was addressed at the meeting between Marat Garayev, Director General of Gazprom Sera and Andrey Klepach, Deputy Minister of Economic Development of Russia on August 21, 2013. The meeting may result in positive outcomes in the coming year.
Modified sulfur binder is a mineral thermoplastic material made of technical sulfur and a modifier. It is obtained by melting sulfur in the carbon dioxide environment, heating the melt to 135–140 °C and adding it to a modifier in the form of unsaturated organic compounds (olefinic hydrocarbons), particularly, dicyclopentadiene in a proportion of 93–98 per cent for sulfur and 2–7 per cent for the modifier. The modifier addition makes it possible to adjust sulfur properties – reduce the melting temperature, inhibit the crystallization process, increase compatibility with filling agents. The resulting substance becomes more enduring (doesn’t break or tear) and ductile.
Sulfur concrete is a composite construction material consisting of sulfur cement, non-reactive aggregates and filling agents. The scope of non-reactive aggregates and filling agents application is vast. Macadam, sand, gravel, smelter slags and other geological materials may be used for this purpose.
Active research studies of sulfur concrete started in North America in 1970s, when it was proved that sulfur concrete and sulfur asphalt were safe for the environment. Later on, in the 1980s–1990s the increase in hydrocarbon production caused higher sulfur recovery, as a by-product of oil and gas. Major oil and gas companies started investigating the new ways of sulfur application, which resulted in new developments for production and application of concrete and asphalt based on sulfur binder. Back at that time its advantages over conventional concrete based on Portland cement were discovered. Later on, experiments showed that the use of modified sulfur was more preferable.
Comparative analysis of sulfur concrete and Portland cement concrete properties
|Property (testing)||Sulfur concrete||Concrete|
|Chemical resistance (to acids), per cent||84||23|
|Cold resistance (at 100 per cent humidity)||300||50|
|Wearing capacity, per cent||3||17|
|Bearing strength, MPa||55–65||15–25|
|Flexing strength, MPa||10–15||6–9|
|Tension strength, MPa||5–7||3–4|
|Time of strength gain||3 hours||28 days|