Key words: 3% clinker; rapid hardening and early strength; replacing cement; micro-expansion; sulfate resistance; Strength stability
0 Introduction
Recently, there are many products with low clinker or no clinker cementitious materials in the market, the principle of which is mainly sulfate excitation, and its essence is gypsum slag cement. Gypsum-slag cement is mainly made of granulated blast furnace slag, mixed with gypsum and a small amount of clinker, without high temperature calcination, which has a significant advantage of low carbon. However, the material has long setting time, low early strength, easy carbonization and dusting on the surface, which restricts its engineering application. The industry standard JC/T 2745-2023 "Gypsum Slag Cement" issued in 2023 provides a basis for the standardized production of this material.
Therefore, in this paper, under the standard framework, through the addition of self-developed admixtures, the proportioning tests with different clinker contents (0,3%, 6%, 9%) were carried out to study their effects on the setting time and strength of gypsum-slag cement. It is proved by our test that both desulfurization gypsum and fluorogypsum can be used to produce gypsum slag cement, but the strength of desulfurization gypsum is lower than that of fluorogypsum in the early and later stages. We will not repeat it here. We can compare it according to the test. Later, we use fluorogypsum as the test raw material for the test. Through the small mill and big mill test, 3% clinker content is the best, which can achieve rapid hardening early strength and stable strength in the later period, and provide a reference for the performance improvement and application of gypsum slag cement.
1. The effect
of different clinker content on the setting time and strength of gypsum slag cement was studied.
1.1. Comprehensive comparison of different clinker content (0, 3%, 6%, The compressive
strength of 0 clinker group was 37.4 Mpa at 3D and 70.2 Mpa at 28d, but the final setting time was still long (375 min), and the strength at 1D was only 7.7 Mpa; The strength of 3% clinker group increased to 13.9 Mpa at 1 day, the final shrinkage was 275 min, the strength of 28 days was 67.5 Mpa, and the performance of early and late stages was balanced; The strength of 6% clinker group is the highest (15. 8 Mpa) at 1 d, but the growth rate slows down in the later period, only 62 at 28 d.
The setting time of 3% clinker group is 147 min for initial setting and 275 min for final setting, and the construction window is reasonable. Compared with the blank group, the final setting time was shortened by 64.
Comprehensive properties: 3% clinker ratio can achieve rapid hardening and early strength (1 d ≥ 10 Mpa, 3 d ≥ 35 Mpa) and later stability (28 d ≥ 67 Mpa) at the lowest clinker consumption. Chloride ion content is low (
0.1.3 Large mill test
equipment: CLM120 × 30 roller press and V-type powder separator are used; Adopt Φ3.
Proportion of selected small mill test 2: clinker 3%, gypsum 15%, slag powder 50%, fly ash 13%, steel slag 12%, stone 5.8%, and activator 1.2%
. After grinding, the specific surface area of the finished product is 443 m ²/kg, and the 45μm sieve residue is 5.6%. The characteristic particle size is 13.5 μm, and the content is less than 3 μm 26.
The performance test of the large mill product shows that
the deviation between the performance of the large mill product and the small mill sample is within 5%, and the setting time and strength meet the design objectives (initial setting ≤ 2. The 3% clinker ratio shows good performance reproducibility under the production grinding equipment, and has the conditions for large-scale promotion. Now take the products produced by the big mill to carry out various concrete tests.
2. Concrete adaptation test
(1) C30 concrete trial mix (15L):
(2) C40 concrete trial mix (15L): (3) Pipe pile concrete adaptation
3. High-strength mortar test
4. Expansion rate test
5. Sulfate resistance test (K method)
Conclusion: The 28-day sulfate resistance coefficient of gypsum slag cement is 1.53; Sulfate erosion resistance coefficient in 60 days is 1.60, which meets the standard of >
0.5. Mortar surface problems
In the past, the fundamental reason for the sanding of gypsum slag cement was the low hydration activity of the system, the insufficient amount of early hydration products and the loose surface structure; At the same time, when the mortar is used, the surface is air-dried quickly, and the slag powder loses its water-based environment before hydration, resulting in low surface strength. In this experiment, the hydration rate of slag was significantly improved by adding self-developed admixture and 3% clinker, and sufficient C-S-H gel and ettringite were rapidly generated in the early stage to fill the pores and compact the surface structure. At the same time, the moderate alkaline environment provided by clinker enhanced the carbonation resistance of the system, and the surface was compact after the strength was greatly improved, so the problem of sanding was fundamentally solved.
Conclusion
(1) Self-developed admixtures can effectively improve the setting and strength properties of gypsum-slag cement. 3% clinker is the best proportion, the standard consistency is 27%, the initial setting time is 158 min, the final setting time is 284 min, the compressive strength of 1 d, 3 d, 7 d, 28 d is 13. 93 MPa, 34. 7 MPa, 50.
(2) Clinker content is not the more the better, when the content is more than 6%, the strength will decrease, and when the content is more than 9%, the strength of clinker at all ages will decrease significantly, and excessive clinker may inhibit the sulfate activation of gypsum on slag.
(3) The product of Φ3.2 m × 13 m ball mill can reach 68.4 MPa, and the chloride ion content of gypsum slag cement is low (≤ 0
) compared with the product of small mill (67.
In the early stage, sufficient C-S-H gel and ettringite are rapidly generated to fill the pores and compact the surface structure, so that the mortar surface is not easy to sand. Through our technical improvement, the performance of early
strength gypsum slag cement has been greatly changed, and the test proves that the application effect of early strength gypsum slag cement in concrete is excellent. Gypsum slag cement is a kind of special cement with unique performance and environmental friendliness. It has irreplaceable advantages in specific applications (large volume, corrosion resistance, underwater engineering) due to its high compressive strength, outstanding flexural strength, low hydration heat, excellent corrosion resistance and excellent impermeability. It is also one of the important technical paths to achieve the goal of "double carbon" in building materials industry.
浙公网安备33010802003254号