100 Questions about Ready-Mix Concrete (41-60)

What is the compressive strength of concrete?

Answer: The compressive strength of concrete is the destructive load that a unit area can withstand when made, cured, and tested under standard methods. The unit is MPa.

What is the flexural strength of concrete?

Answer: The strength obtained by breaking a 150mm×150mm×550mm specimen after standard curing in a flexural test fixture is called flexural strength, with the unit being MPa. High-grade highway pavements require testing the flexural strength of concrete.

What is the impermeability of concrete?

Answer: It refers to the ability of concrete to resist the penetration of water under pressure. Basements and reservoirs require good impermeability.

How many common impermeability grades are there for waterproof concrete?

Answer: There are four common impermeability grades: S6, S8, S10, S12 (old notation) or P6, P8, P10, P12 (new notation). 'S' is the first capital letter of the pinyin for "渗" (shēn, meaning seep), and 'P' is the first capital letter of the English word "impermeable".

What is the frost resistance of concrete?

Answer: It refers to the ability of concrete to resist repeated freeze-thaw cycles. The frost resistance grades are F100, F150, F200, where 'F' represents frost resistance, and the number indicates the number of freeze-thaw cycles between -15℃ and room temperature.

What is the difference between the frost resistance and antifreeze properties of concrete?

Answer: The frost resistance of concrete refers to its ability to resist repeated freeze-thaw cycles after reaching its design strength, while the antifreeze property of concrete refers to the ability of the concrete mixture to prevent low-temperature damage during the setting and hardening process.

What is the durability of concrete?

Answer: It refers to the ability of concrete to resist weathering, water penetration, and erosion by harmful substances. The stronger this ability, the better the durability.

Why should customers be treated as gods?

Answer: Because customers create the production conditions for ready-mix concrete companies. Only by treating them as gods can we have more production tasks and earn more money from them. Customers are like our gods of wealth.

How should customers be treated?

Answer: First, treat customers with civilized and polite behavior. Greet them with "hello" before asking questions, use a kind and not rude tone, and speak politely and truthfully; do what you can immediately, don't be lazy or procrastinate; meet reasonable requests, and politely refuse if temporarily unable to fulfill them.

Why can't too many trucks be dispatched at the beginning of pumping concrete?

Answer: Because the conditions at the construction site vary greatly. Some may not have finished inspecting the steel bars, or may not be ready. Even without these problems, there is still the issue of whether the pumped concrete is easy to pump. Start by sending one truck, and then another after 15-20 minutes. When the first truck arrives at the site, understand the site conditions. If everything goes smoothly and the pumping is normal, continuous dispatching can be done; if the site is not ready, do not dispatch; if the concrete has poor pumpability, immediately notify the laboratory director to adjust the mix ratio before dispatching.

What tasks should the dispatcher pay attention to?

Answer: (A) Issue task orders and organize production rationally.

Answer: (B) Reasonably dispatch vehicles to ensure that there is no backlog at the construction site, no interruptions, and continuous production.

Answer: (C) Properly fill out transportation slips: the mix number, weight ratio, and initial slump must be consistent with the data from the laboratory.

What matters should the dispatcher clarify when receiving a task plan?

Answer: When the purchaser calls to report the plan, the following matters should be clarified: construction unit, project name, pouring location, delivery slump, concrete strength grade, planned quantity, formwork method, pouring speed (minutes/truck), contact person's phone number, any special requirements, such as the use of a pump truck (pump truck arrival time), and the planned concrete arrival time.

What should be done if some construction sites misestimate the quantity, leaving some concrete left over?

Answer: Immediately pull it back to the mixing plant to weigh the quantity, adjust according to the current production tasks, and ask the laboratory director for specific adjustment methods.

What should be done if special circumstances prevent pouring at some construction sites when the concrete arrives?

Answer: Contact other stations in the company to see if there are production tasks of the same grade and type. If so, let the driver go to that station to exchange the transport slip and then send it to the construction site. If there are no construction sites of the same grade and type, immediately notify the laboratory director to adjust the concrete in that truck to a grade and type with a task.

How to prevent under-delivery?

Answer: The production control personnel should pay attention to the change in water usage during production. When the water usage is 10kg or more less than the water usage set in the production mix ratio, the amount of water should be added to the sand. The dispatcher should check the factory apparent density (bulk density) of concrete for every 40m3 or more of production. If the difference from the design value is more than ±10kg/m3, the control room should be notified to find the cause, which may be due to inaccurate batching scales, and immediate calibration is required.

What should be done if some construction sites report under-delivery of concrete?

Answer: Immediately notify the production manager and laboratory director to find the cause. First, check the computer production records to see if there is an excessively large negative deviation, or if only water was reduced without adding sand; second, check the pouring site to see if there is any formwork swelling, excessively thick cast-in-place slab, or spillage and waste; third, carefully calculate whether the planned quantity is incorrect.

How should materials be loaded if the sand in the material yard has a mix of coarse and fine sand?

Answer: If using one silo for loading, load one scoop of coarse sand followed by one scoop of fine sand alternately. If using two silos, one is for coarse sand and the other for fine sand.

How should materials be loaded when there is a significant difference in the size of the stones at the No. 58 material yard?

Answer: Use two stone bins for loading, one for larger stones and one for smaller stones.

What should be done if a truckload of wet sand is unloaded at the material yard while concrete is being produced?

Answer: Immediately shovel it aside. Strictly prohibit loading the newly delivered wet sand into the sand bin. Continue using the sand currently in use.

How should materials be loaded after heavy rain causes water accumulation in the material yard?

Answer: Shovel the materials from above the water level. Strictly prohibit shoveling water into the hopper and loading it into the bin.