Two hundred years ago, the British invented Portland cement and made a significant contribution to the construction of human civilization. However, in the long-term use found that Portland cement still has performance defects, mainly seawater corrosion, saline-alkali erosion and can not be negative temperature construction and other issues.

In the 1970 s and 1980 s, the Chinese successively invented sulphoaluminate cement and ferroaluminate cement. Compared with Portland cement, this kind of cement belongs to different mineral systems. See Table1.

Table1 Main minerals of different cement varieties

From Table1It can be seen that the main minerals of Portland cement areC₃SThe main minerals of sulphoaluminate cement areC₄A₃SThe main mineral of iron aluminate cement isC₄A₃SandC₆AF₂. Different mineral compositions give different properties to cement.

The corrosion resistance of cement is usuallyK_nValue representation.K_nThe value is the flexural strength of the test body cured in corrosive solution.R_Liquiddivided by the flexural strength of the specimen cured in fresh waterR_Water, I .e.K_n=R_Liquid/R_Water.nrefers to the curing age, generally used28day,6months,12months or24Months.KThe physical meaning of a value is that its numeric value is less1, indicating that the cement test body has been corroded in the corrosion liquid, the lower the value, the greater the degree of corrosion; the value is greater1, indicating that the cement test body is not corroded, the larger the value, the higher the strength growth of the cement test body in the corrosive fluid.K_nThe value is the most accurate indicator of whether the cement hydration test body will corrode or the degree of corrosion. Different varieties of cement in typical corrosion solutionKValues are shown in Table2Table3.

Table2 Curing of different varieties of cement in saline-alkali soil immersion water in Lop Nur areaK6mValue

From Table2It can be seen that the sulphoaluminate cement is soaked with water in different saline-alkali soils.6After months, its strength will not decrease, but significantly increased; ordinary Portland cement is greatly reduced.

Table3 Different varieties of cement in Dongshan Island sea water conservationKnValue

From Table3It can be concluded that the iron aluminate cement in Dongshan Island seawater immersion28Days later, instead of decreasing, its intensity increased3%Soak12increased after a month.9%Soak24A month later, it increased further.17%; Ordinary Portland cement strength is significantly reduced, soaking28Days after the decline23%Soak12Decreased after a month29%Soak24months later, it fell further.42%.

1982In the autumn of 2008, researchers placed self-stressing tubes made of Portland cement and ferroaluminate cement in the same period on Xipu Bay Beach, Dongshan Island, Fujian Province, for natural exposure tests.2023The year inspection found that the Portland cement pipe has been severely corroded and has almost no strength (see Figure1), the internal reinforcement is seriously corroded; However, there is no corrosion in the ferroaluminate cement pipe, and there is no obvious corrosion in the internal reinforcement. The strength test results of cutting and sampling of the cement pipe are shown in the table.4.

Figure1 Natural seawater exposure test of different varieties of cement pipes41Comparison of corrosion after the year

Table4 Natural Exposure Test of Self-stressed Pipe of Different Cement Varieties in Seawater of Dongshan Island41Strength value after year

A large number of laboratory data and more than 40 years of practical engineering cases have shown that iron aluminate cement has the special performance of seawater, salt and alkali corrosion.

Different cement varieties show different properties because of their different cement hydration mineral composition.

Table5 Hydrated mineral composition of different cement varieties

From Table5It can be seen that the main hydrated minerals of sulphoaluminate cement are very different from Portland cement, and the main hydrated minerals of Portland cement mainly containCa(OH)₂ Leaching occurs in the action of soaking liquid and seawater, and the structure of cement stone is destroyed, which leads to corrosion of cement concrete. The main hydrated minerals of sulphoaluminate cement areC₃A·3CaSO₄·32H₂O, is very stable in immersion liquid and seawater, so the cement concrete remains intact.

From Table5It can also be concluded that the main hydrated minerals of sulphoaluminate cement are removed.C₃A·3CaSO₄·32H₂Oalso contains low alkalinity hydrated calcium silicateCSH(І)The alkalinity of the liquid phase ispH 11.5~12.0. Due to the low alkalinity of the liquid phase, the early rust of steel bars and the powdery surface of cement stone are produced; the main hydration products of ferroaluminate cement are the same as sulphoaluminate cement.C₃A·3CaSO₄·32H₂OThe difference is that the calcium silicate hydrate contained in it is high alkalinity.CSH(II)The liquid phase alkalinity is higherpH 12.0~12.5Under this condition, there will be no defects such as early rust spots of steel bars and powder on the surface of cement stone.

Ferroaluminate cement is free from seawater and saline-alkali corrosion, and has no defects such as early rust spots and surface powdery of steel bars.

The exotherm of sulphoaluminate and ferroaluminate cements usually occurs after the start of hydration.12Within hours (see figure2), which makes them have the characteristics of negative temperature construction. The average temperature of sulphoaluminate cement reached in summer-25 ℃The construction of the Antarctic construction station. The hydration heat of ferroaluminate cement is earlier, and it has better negative temperature construction performance.

Figure2 Hydration heat curves of different cement varieties

After decades of research and development by the scientific research team of the key laboratory of ferroaluminate cement, it has been proved that ferroaluminate cement has the performance advantages of seawater, saline-alkali non-corrosion and negative temperature construction, as well as outstanding energy-saving and low-carbon characteristics. The development of ferroaluminate cement industry is an important part of the development of new quality productivity in the building materials industry.

2020Year and2022In 2003, Vice Premier He Lifeng made two important instructions on the work of the ferroaluminate cement industry when he was the director of the National Development and Reform Commission. The national development and Reform Commission has supported the demonstration application of ferroaluminate cement in Hualong No.1 nuclear power plant through major special projects. At present, the project has been successfully completed and a series of important achievements have been made.2023In 2002, the General Office of the National Development and Reform Commission wrote that it would continue to support the demonstration and application of ferroaluminate cement in major national projects such as nuclear power plants.

The state attaches great importance to the technical application of ferroaluminate cement products.2023As one of the major technical equipment products, iron aluminate cement is included in the relevant national implementation plan, which is also the only product technology included in the building materials industry. The technical unit is an institution managed by the China Building Materials Federation under the State-owned Assets Supervision and Administration Commission of the State Council.--Technical supervision and research center for building materials industry.

It can be predicted that ferroaluminate cement will play a great role in the construction of human civilization in the future.

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