Expansion agent

High Efficiency Concrete Expansion Agent with Low Alkali Content and Low Addition level ZY®

ZY concrete expansion agent, is one of the important achievements with patent right of China Building Material Academy (CBMA), which was awarded the second prize of National Awards of Science and Technology Progress and popularized as the key scientific payoffs and the recommended products used to construct the Xiaokang residential quarters by the Ministry of Construction. ZY is a kind of water-resisting admixture coupled with crack resisting. It has been used in thousands of water-resisting and crack-resisting engineering in countrywide and came to the top since it adopted the identification at ministry level in 1991.

Now the forth generation of ZY concrete expansion agent, the series of ZY high efficiency concrete expansion agent with low alkali content and low addition level, has been sold on the market. Its patent number is ZL91110609X. The ZY has higher expansivity and lower alkali content than general UEA sold on the market. The series of ZY have 5 types: general type (Ⅰ), pumping and retarding type (Ⅱ), pumping and high early strength type (Ⅲ), frost-resisting type (Ⅳ), and high-performance type (Ⅴ). All of them accord with the standard of building material industry “Concrete Expansion Agent” numbered JC476-1998 and others related to concrete additive.

Perhaps newer and better building materials are just what you need and a wider market is expected for us. We are waiting for more customers and friends and ZY will certainly become the link contacting with each other.

New Concept of Waterproofing

The reasons causing crack in common concrete are complicated and for materials, the main one is drying shrinkage of the concrete and shrinkage due to temperature difference between surface and center of the concrete. So a kind of expansion agent (ZY), with a main function of compensating shrinkage, was successfully manufactured in CBMA. When ZY, general cement concrete and water are blended and stirred, a great deal of expansive crystalline hydrate, calcium sulphoaluminate hydrate (C3A·3CaSO₄·32H₂O), are produced and a tendency of expansion in the concrete is visualized. Because of the compact confinement from the steel bar and other parts in adjacent place, a compressive prestress of 0.2—0.7Mpa is produced in the construction, which balances the tensile stress from the concrete shrinking in process of its hardening. Now “The Method of Compensating the Shrinkage of Concrete in Engineering Application” has been listed as a national level method in engineering application (YJGF22-92). This means that the concrete with ZY is an important breakthrough in self-water-resisting of the structure in our country.

By the stipulations of ministry of construction, water-resisting engineering is divided into four grades according to the importance. No matter which grade we choose, the self-water-resisting of structure is essential, because the aging and breaking phenomena after all is in existence for the outer-layer water-resisting, used to coiled materials and coating materials and the seepage caused in the construction is a nonnegligible problem too. When general concrete is used as structural materials, the construction will lose the final line of defence in case it shrinks and cracks and this is a main reason that buildings seep.

According to our practice for many years, we bring forward such a new concept that for any water-resisting structure of concrete, the crack-resistance is more important than the seep-resistance or there will be no seeping if no cracking. The shrinkage compensating concrete is a kind of ideal material that proves an important ensurance to the self-water-resisting of structure.

The Physicochemical Properties and Alkali Content of ZY

1) Chemical elements and alkali content

Table 1. Chemical elements and alkali content:

3) The properties of concrete with ZY

The series of ZY products with multi functional was composed of ZY and special chemical additive and the main property of concrete with them was showed table 4. All of technical indicators were up to or above national related standards. Its characteristics were stated as follows:

1. Good working performance: Solidifying-slowly, water-decreased, easily flowing, less wastage of collapse degree, and easily-transported with pump.
2. Fine crack-resistance and seep-resistance: high effect of expansion, grade of seep-resistance is more than S30.
3. Hydration heat is decreased, the hydration heat peak and the initial time of shrinking is delayed and so the shrinkage, caused by the temperature’s difference in concrete, and the cracking is weakened and restrained.
4. When it is used in concrete the concrete needn’t add any others at all. So an easier operating with less procedures, less mistakes brings into existence.

It can well be compatible with cement and easy to be used in a stirring station or in situ.

Table 4. The main behaviors of the concrete with multi-function ZY:
 

Unique Properties of ZY Production

1.  Low addition level Limited expansion ratio that adding 6% ZY surpasses that adding 12% of general UEA sold on the market, achieves 0.03~0.04%. 
2.  Low alkali content The alkali content R2O ( Na₂O+0.658K₂O ) is 0.3~0.4%,lower than 1.7~2.2% for adding UEA.
3.  High activity It doesn’t influence the early and later strength, indeed achieves equal replacement of cement.
4.  No slump constant loss Its adaptability for cement and other concrete addition is better, and workability is good.

The Application of ZY

General concrete is a kind of widely used building material. Due to quite low tensile strength, very small limited elongation rate, it is easy to produce cracks in the process of drying shrinkage, slow shape change and temperature difference, which will lead to seeping and corroding to steel bar and then weakens the functions and lives-time of concrete. So in the engineering field home and abroad, various researches and practices have been taken from material, constructing design and so on. On material aspect, a application of shrinkage compensating concrete is thought as essential by specialists from many countries and this kind of material is an ideal one to avoid cracking and seeping. The shrinkage compensating concrete containing ZY, is mainly applied in the following four fields.

1) Realize self-waterproofing of the concrete structure

In general concrete it is easy to produce a shrinking crack that forms a dypass of seeping and the mono-waterproof function of the concrete is frustrated. So an attention should be at first paid to the crack-resisting that is more essential than seep-resisting. When ZY added into concrete, the crack of concrete is efficiently prevented .On the other hand, because the expansive crystal performed by the reaction between ZY and cement, it can improve micro-structure and fill and block up capillary bores, the seep-resistance of material itself is enhanced too. The self-waterproofing for concrete structure can be realized by the use of ZY and outer waterproofing process can be canceled. So the waterproofing costs is reduced to one third. Now “The Method for Application of Shrinkage Compensating Concrete in Structural Engineering” has been listed as a national level method in engineering application (YJGF22-92). This means that the concrete with ZY is an important breakthrough in structural self-waterproofing technology in China.

2) Cancel the post-cast joint of a super-long structure

Because of shrinkage and accumulation of shrinkage, once casting to a construction with over huge size may cause cracks in general concrete. So a joint for shrinkage must be reserved per 30-40m , which is called as the post-cast joint usually cast again after 40-60 days. All this may cause a delayed term of engineering, a trouble cleaning work and a hidden danger of seeping.

According to the shrinkage compensating principle of expansive concrete, it is feasible that the joint for shrinkage may be canceled in a underground engineering through a great deal of research and practice when the concrete is in the size of 60 meter, and when over 60 meter, the joint may be replaced by the expansion strengthened zone added with ZY. The strengthened zone usually with a width of 2 meter, is set at the position where the shrinking stress is biggest, the shrinkage of concrete will be compensated by increasing the addition of ZY in the zone (addition amount from 6-8% to 8-10%, expansion ratio is 4~6x10-4). As the high assay of ZY could decrease the strength of concrete, the strength grade of concrete in the zone is 5Mpa higher than that in both sides. As the limitations by steel bar and both sides, the strength in strengthened zone is enhanced actually. The strengthened zone should be cured not less than 14 days.

Through engineering practice, it is indicated that a continuous casting of supper-long construction is realizable. This method not only may be applied to tunnel, underground, and hydro-engineering but also to tall buildings without waterproofing requirement to reduce the usage of mould boards and quicken construction progress. This technology is counted the origination at home and abroad (patent number is 93117132.6).

3) Control the crack caused by the difference of temperature in a large size concrete structure

It is very important to control the temperature difference between the surface and the center of large size concrete. The temperature difference is required less than 25℃ for general concrete, otherwise cracks (crack from cooling period) will be caused by the stress from temperature difference. When ZY concrete is used, the difference of temperature may extended to 30-35 ℃.

This means that in process of constructing of a large size concrete, as the use of ZY, the requirement to controlling temperature difference is weakened. It is not necessary to cool aggregate and set cooling pipeline in concrete and the constructing costs are greatly reduced. This technology has been applied to many buildings and satisfactory effects have been taken, such as Beijing West Station, Wuhan International Trade Building, Beijing Baoding Plaza, Xinfeng Plaza, Shanghai Wold-trade Center, and some basic engineering with 2-4m thickness in Tianjin Rolling Mill.

4) Stiff roof covering

For a stiff waterproof roof covering, it has advantages of simple structure, low cost, fine water resistance and fine durability, but a post-crack that might causes seeping would exist in the general concrete. This disadvantage can be overcome by the use of concrete added with ZY. This new technology has been applied to the constructing of staff, waterproof roof covering near 2 million sq. m. in Jiangsu, Zhejiang, Fujian, Guangdong, Guangxi, Beijing, Xi’an, Wulumuqi and so on and a fine effect has been taken. Through years practice and argumentation from experts, the stiff roof covering with shrinkage compensating has been list as “The Technology Specification of Roof Engineering” (GB50207-94), issued by Ministry of Construction.

5) High Performance Concrete

As the continuous appearance of tall buildings, large span bridges, the constructions in ocean, and high-speed highways, there are more and more requirements to high performance concrete. For a high performance concrete, it not only has excellent mechanical properties but also fine working properties and great durability. Nowadays superplasticizer, pulverized silicate ash or thin powder of slag and pulverized fuel ash is very generally adopted in process of the fabrication of high performance concrete, but all of them increase the shrinkage of concrete. For compensating shrinkage , ZY expansion agent becomes the preferred addition agent.

The Specific Use of ZY

ZY may be applied to any concrete engineering and cement products in which crack resistance, seeping resistance, and so on are required. Especially in the following:

1.  Underground construction: subway, underground parking, underground storeroom, tunnel, mine, civil air defence, subway crossing, underground parts of foundation, and so on.
2.  Constructing: water tank, swimming pool, water tower, storage tank, large size container, barn, oil tank, thesaurus in a cavern, and so on.
3.  Self-waterproof roof covering, seep-resisting layer with sand grout, vapor-proof layer with sand grout.
4.  The anchor connection between precast units or frame structures, conduit joint, grouting and backfilling material for the post-cast joint of construction and so on.
5.  The grouting material used to cast contractively between barb bolt, pedestal and foundation of concrete.
6.  Mortar used for the protecting layer within cast iron pipe and steel pipe.
7.  Cement products, concrete water pipe with self-stress, or pre-stress, drainpipe of concrete or steel reinforced concrete, floor slab, pillar, beam, waterproof roof slab, and so on.
8.  Some important building that great crack resistance and perfect appearance is required, such as bleachers in stadium, statue in city, museum, hotel, and so on.
9.  The road surface of highway, the concrete surface layer of bridge, culvert.
10.  Vertical shaft with high strength and high seeping resistance, the concrete used to filling the back-slot in a main dam.

The Direction for Use of ZY

1.  According to the strength grade and the seeping resistance of concrete, the stirring way of concrete, and constructing season, a right type of ZY should be selected. Usually other chemical additives are not necessary for multi-function ZY. But for general type ZY (Ⅰ), a right stirring way and some proper chemical additive is essential.
2.  The calculation of mixing proportion for shrinkage compensating concrete added with ZY is alike as that in general concrete, but for waterproof engineering, the dosage of cement should be increased about 10% and the sand ratio should be controlled in the scope of 36-40%. Above this basis, ZY can well be added into concrete and the proportion of water and cement can be adjusted by concrete slum, usually the water/cement ratio should be less than 0.5.
3.  The addition level of ZY is determined by the equation, E/(E+C), C—cement, E—ZY, usually the value is 5-8% and when concrete used to the filling of post-cast joint or strengthened zone, the value should be in the scope of 8-10%.
4.  The error of weighing ZY should be controlled below 0.5%. ZY had better be put into kneading mill together with other material.
5.  Compared with general concrete, for field-stirred concrete, the stirring time of concrete with ZY should be delayed 30-60 second, and for non-field-stirred concrete, such as commercial concrete, the stirring time might not be delayed at all.
6.  If the distance of concrete transportation is far, or the temperature of weather is high, a few superplasticizer may be added in situ when the slum of concrete is less than 12cm. After a quick stirring, the concrete is sent to where it should be, but an adding of water is strictly forbidden.
7.  ZY concrete is mainly applied to the engineering with structure self-waterproofing , so an attention should be paid to being a dense structure for the concrete, the chattering is neither missed out in some parts, nor overladen. The wiping should be, at full tilt, repeated over three times before the final setting concrete in order to avoid a crack out of subsidence.
8.  A curing should be undertaken 12-24hr after the concrete has hardened and maintained not less than 14 days. A curing with temperature keeping and dampness keeping has to be undertaken for the concrete cast in winter and the concrete with a large size.
9.  As the layer of concrete, lying on the surface of a wall, is thin and its curing is difficult too, it will cause a too fast drop of temperature and shrinking cracks in the concrete for the formworks to be dismounted untimely. In normal temperature, the formworks may be loosened and move about 2-3mm one day after the concrete is cast, and the curing to concrete should be at least maintained for 14 days. The time of dismounting formworks is 3 days to C30 concrete, 7 days to C40 concrete, and 10 days to C50 and above concrete.
10.  A few small holes and cracks caused by an ill constructing may be patched with mortar added with ZY (sand to cement ratio being one to two), and a 10-15mm waterproof layer has to be finished with the same mortar for horizontal or upright joint in the outer wall.
11.  The distance between post-cast joints can be increased to 60 meter when shrinkage compensating concrete added with ZY used. In fact, by means of the new technology of non-joint design and constructing, the distance between post-cast joints may reach up to 100-150 meter and a running casting of concrete comes to realization in a construction with great large size.
12.  ZY concrete can not be used in the engineering that chronically stands in the temperature over 80 ℃.
13.  ZY should be stored in a drying and ventilating circumstance. Caution against wet. The keeping time of ZY is one year in a drying and ventilating circumstance, but ZY should be undertaken a physical examination again over 6 months storage.

Table 5. The reference table of the mixing proportions of concrete with ZY:
 

* 1. This table is just applcable to the concrete with general type ZY;
2. If the multifunction ZY is used, no other additive is necessary;
3.In the concrete with pumping type ZY ,the pulverized fuel ash (Ⅱgrade) may be used to replace 10-12% of cement.
 

Expansion agent used in wastewater treatment project