The setting time of Mg3(PO4)2 cement of borax and dipotassium hydrogen phosphate

The invention realizes the setting time of Mg3(PO4)2 cement of borax and dipotassium hydrogen phosphate by composite regulation. Borax is a commonly used retarder in magnesium cement, but the slow setting of borax is often at the cost of early deterioration of behavior. On the one hand, the potassium salt of di (2-ethylhexyl) phosphate and potassium dihydrogen phosphate form a buffer solution after adding potassium phosphate for many times, which improves the pH value of the system and delays the setting of magnesium phosphate cement slurry; On the other hand, dipotassium hydrogen phosphate (the heat of K2HPO4 · 3H2O is selected) is absorbed in the crystallization process, and the water is lost, which reduces the temperature of the system and achieves the effect of slow condensation. At the same time, experimental research shows that when dipotassium hydrogen phosphate has a retarding effect on water, the early mechanical properties of the mud can be improved. With the increase of borax content, the setting time of magnesium phosphate cement increases gradually, but it is not conducive to the early strength; On this basis, adding potassium hydrogen phosphate again can further delay the setting of cement, and at the early phase, the mechanical properties have no adverse effect. Moreover, there are strict requirements for the addition ratio of dipotassium hydrogen phosphate and dipotassium hydrogen phosphate. If the ratio is too small, there is no delay effect. If the ratio is too large, the delay effect is not obvious due to the balance of phosphate buffer.

Besides delaying the condensation of magnesium phosphate cement, potassium hydrogen phosphate can also participate in the hydration process of magnesium phosphate cement to generate KOH crystals. The specific reaction equation is as follows: MgO+K2HPO4 · 3 h2o+3 h2o → MgKPO4 · 6 water+KOH,

Therefore, the repair mortar has a slight expansion energy, and the shrinkage cracking in the later repair caused by the failure of repair and other reasons is avoided. Question.

The invention can guarantee the water resistance of the repair mortar mainly due to the matching of mineral admixture and mixture. Mineral admixtures such as fly ash and silica fume in fine pulverized coal can not only participate in the hydration reaction in magnesium phosphate cement mortar, but also fill the holes in the mortar matrix. The dense matrix prevents the invasion of external moisture and the loss of internal components. When mixed with mineral admixtures with different particle sizes, a compact filler can be formed in the mortar. For a more simple mix, the performance reference mark of mortar can be improved more effectively. In addition, mineral admixtures can also participate in the water solubility of silicate system to improve the bonding performance between repair mortar and old concrete.

Compared with the prior art, the invention has the following advantages:

1) The early strength is high, and the compressive/fracture strength in 1h can reach about 20.0/3.50MPa, and the concrete structure can be recovered in 1-2 hours;

2) The setting time is controllable: in the patented technology of the invention, the setting retarder borax is adjusted by adding the composite action of di (2-ethylhexyl) calcium phosphate potassium salt and calcium phosphate, and the purpose of controlling the setting time of repair mortar can be achieved through the composite action between the three and adjusting the proportion of their addition

3) K When 2hpo4 is used to adjust the curing, the repair mortar can show a slight expansion characteristic, with good volume stability, and can avoid cracking caused by the shrinkage of the repair surface in the later period;

4) The new and old concrete have good adaptability and high bond strength;

5) The re mixing of mineral admixtures can significantly improve the water resistance of Mg3(PO4)2 cement based rapid repair mortar, and high water resistance is the guarantee of the long durability of the repair mortar;

6) Mineral admixtures use a wide range of materials, which are extracted from industrial wastes requiring additional processing. They not only have low cost, but also increase the use of industrial wastes, making them more environmentally friendly.