Difficult problems and countermeasures of pumping concrete

1. Adaptability of concrete admixture to cement (1) The stability of cement ore leads to the stability of mineral components and affects the adaptability of concrete admixture to cement. (2) Cement manufacturing processes such as vertical kilns and rotary kilns, manageability of quenching measures in cooling systems, and temperature during gypsum crushing affect the adaptability of cement and concrete admixtures to cement. .. (3) Ability to adsorb admixture to cement: C3A> C4AF> C3S> C2S. The hydration rate of cement is directly related to the mineral composition. (4) When cement is stored for a certain period of time, the temperature drops, the high temperature adaptability of the concrete admixture improves, f-CaO absorbs moisture in the air and converts it to Ca (OH) 2, and CO2 in the air. Absorbs and converts to CaCO3, which reduces Mwo, improves concrete workability, slows slump loss of freshly mixed concrete, and slightly increases concrete setting time. (5) The water demand of ordinary Portland cement is slightly larger than that of slag cement, and the water retention is good, but the slump loss is generally fast. (6) Cement with a high C3A content has fast slump loss and good water retention. (7) Hydrophilic admixture for cement has high water retention, and pozzolan cement has low water retention and easily bleeds. (8) Temperature and humidity directly affect the adaptability of concrete admixtures to cement. (9) Sand, stone gradients, and the ratio of sand, stone, water, and adhesive in the mixing ratio also affect the adaptability of concrete admixtures to cement. 2. Reasons and solutions for concrete bleeding and segregation problems 2.1 Reasons (1) The larger the cement, the easier it is to bleed. The content of C3A in cement is low and it is easy to bleed. Standard cement consistency is small and easy to bleed; slag is easier to bleed than regular silica; Pozzolan Portland cement is easier to bleed; Grade I fly ash is easier to bleed; cement mixed with non-hydrophilic mixed material bleeds It’s easy to do. (2) The amount of cement is small and it easily bleeds. (3) Low-grade cement is easier to bleed than high-grade cement (same amount). (4) When the same grade of concrete is used, concrete using high grade cement is more likely to bleed than concrete using low grade cement. (5) Concrete that consumes a large amount of water per unit is prone to bleeding and segregation. (6) Low-strength concrete tends to bleed (normal). (7) Concrete with a small proportion of sand is prone to bleeding and segregation. (8) Continuous grain size crushed stone is smaller than concrete bleeding of single size crushed stone. (9) Concrete with low water retention, thickening, and air entrainment of concrete admixtures tends to bleed. (10) Concrete that is super-mixed with a concrete admixture is prone to bleeding and segregation. 2.2 Solution (1) The basic method is to reduce the unit water consumption. (2) Increase the proportion of sand and select the appropriate proportion of sand. (3) Increase the amount of water and cement or mix with the appropriate amount of fly ash II and III. (4) Continuously inclined crushed stone is used, and the content of needle flakes is low. (5) Improve the performance of the concrete admixture to improve water retention and viscosity, or reduce the amount of concrete admixture appropriately (on-site only). If the mixing station reduces the amount of concrete admixture, concrete collapse can occur. .. A new problem with rapid fluid retention. 3. Reasons and solutions for scratches or compaction of the bottom of pump concrete 3.1 Reasons (1) Heavy bleeding concrete is prone to scratches or compaction (stick pots). (2) Concrete containing a lot of cement is easily scratched at the bottom. (3) Concrete containing a large amount of concrete admixture is easily scratched at the bottom. (4) The proportion of sand is small, and concrete is easy to compact. (5) Concrete admixtures have a high water reduction rate and bleed rate, and concrete with low water retention, thickening, and air entrainment effects is prone to scratches and compaction. 3.2 Solution (1) Reduce unit water consumption. (2) Increase the proportion of sand. (3) Add an appropriate amount of admixture such as fly ash to reduce the amount of cement. (4) Reduce the amount of concrete admixture. (5) Improves air entrainment, thickening and water retention functions of concrete admixtures. 4. Reasons and solutions for pumping concrete slump loss problem 4.1 Reasons (1) Poor adaptability of concrete admixtures and cement causes rapid concrete slump loss. (2) Insufficient amount of concrete admixture, delay and plastic preservation effect is not ideal. (3) In hot weather, certain additives fail at high temperatures, water evaporates rapidly, air bubbles overflow, and fresh concrete slumps are rapidly lost. (4) The initial concrete slump is too small and the unit water consumption is too low, so the solubility of gypsum in cement hydration is insufficient. In general, the loss of sl0 ≥ 20 cm concrete slump is slow and vice versa. (5) Generally, the order of slump loss rate is high alumina cement> Portland cement> ordinary Portland cement> slag Portland cement> miscible cement. (6) Inadequate coordination between the construction site and the mixing station, too long squeezing and congestion time, resulting in excessive loss of concrete slump. 4.2 Solution (1) Adjust the composition of the concrete admixture to make it compatible with cement. Be sure to test the adaptability of concrete admixtures and cements before construction. (2) Adjust the mixing ratio of concrete, increase the ratio of sand and water consumption, and adjust the initial slump of concrete to 20 cm or more. (3) Add an appropriate amount of fly ash to replace some of the cement. (4) Increase the amount of concrete admixture appropriately (especially when the temperature is much higher than usual). (5) Prevent water from evaporating too quickly and bubbles from overflowing too quickly. (6) Select slag cement or pozzolan cement. (7) Improve the water retention / cooling system for concrete transport vehicles. 5. Reasons and solutions for pumping concrete pipe blockage 5.1 Reasons (1) The workability of concrete is poor, segregation occurs, and concrete is scattered. (2) The slump of the concrete mixture is small (dry adhesiveness). (3) The concrete mixture grabs the bottom and hardens. (4) Single grain stone is used, the grain size of the stone is too large, and the diameter of the pump pipe is small. (5) There are many pebbles needles and flakes. (6) The pressure on the pump truck is insufficient or the pipeline is not tightly sealed. (7) Ratio of low cementum material to low sand. (8) There are too many elbows. (9) Foreign matter in the tube has not been removed. (10) When concrete is mixed, unevenness occurs, cement aggregates, and it becomes a cement slurry without loosening. (11) The pipe wall was not lubricated with mortar before the concrete was pumped for the first time. 5.2 Solution (1) Check the proximity of the concrete transport pipeline and the operating performance of the pump truck to make it in good working condition. (2) Check the piping layout and make sure that the bend is 90 ° or less. (3) Before pumping concrete, the pipeline must be lubricated with mortar. (4) Check if the grain size and shape of the stone meet the specifications and pump requirements. (5) Check the workability of the concrete mixture at the pump inlet, whether the sand ratio is appropriate, whether there is a large cement block, whether the mixture has bleeding, scratches, hardening, etc., and take corresponding measures. (See Specific Bleeding and Separation Issues). (6) Check if the concrete slump and cohesiveness at the pump inlet are sufficient. If the slump is inadequate, increase the amount of concrete admixture appropriately or add an appropriate amount of high efficiency water reducing agent. Pump inlet, for concrete If cohesiveness is inadequate, increase the proportion of sand by the appropriate amount or add the appropriate amount of Grade II fly ash. (7) Check if the initial slump of concrete is 20 cm or more. If concrete slump loss occurs due to a concrete pump blockage phenomenon, the concrete loss problem must first be resolved (see Slump Loss Problem). ..

Article reprinted on this site:https://alloy.wiki/difficult-problems-and-countermeasures-of-pumping-concrete/