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  What is the Allowed Time for the Concrete Discharge? There is always confusion on site about the required time for the discharge of concrete. Some say it is 60 minutes, 90 minutes, 120 minutes, etc. Which is it? One time, we had cast the wall below ground. It was in the second basement, and due to the distance of the wall from the truck mixer outside the building, it took several minutes to reach the wall using the bobcat. The consultant found out that the concrete had expired and he said to the project engineer, “Engineer, the concrete has expired!” He then told the project engineer, “You have to return the concrete or throw it out from here!” The project engineer replied, shouting “No! As per the standard time… Blah! Blah! Blah!” And so on and so forth. You would probably be confused listening to this, if you heard the two voices, as they barely differed from each other. The consultant took the delivery notes of the concrete and he said, “Engineer, I will raise an NCR about thi...

  Hot Weather Concreting - Any operation of concreting done at atmospheric temperatures above 40°C or any operation of concreting (other than steam curing) where the temperature of concrete at time of its placement is expected to be beyond 40°0. Effects Of Hot Weather On Concrete : Effects of hot weather on concrete, in the absence of special precaution, may be briefly described as follows: a) Accelerated Setting - High temperature increases the rate or setting of the concrete. The duration of time during which the concrete can be handled is reduced. Quick stiffening may necessitate undesirable retempering by addition of water. It may also result in cold joints. b) Reduction in strength - High temperature results in the increase of the quantity of mixing water to maintain the workability with consequent reduction in strength. c) Increased tendency to crack - Either before or after hardening plastic shrinkage cracks may form in the partially hardened concrete due to rapid evaporati...

Understanding Concrete Cover and Why We Need It In construction, whether in bridges, piers, or residential houses, we use concrete for vertical or horizontal elements, and huge volumes of concrete are used especially in the construction of a high-rise building. When you talked about concrete, the other important material involved is “ steel reinforcement .” When these two important materials bend together, then you need to start checking the concrete cover for the various concrete elements to be cast in your project. A concrete cover contributes to the integrity and soundness of the building. If not done well, it may also cause failure to the building and reduce the durability of the structure. You must observe concrete covers when constructing the pile foundations and/ or footings to the ground beams and slab-on-grade, because these types of concrete elements are exposed to weathering, and are the most likely to experience uplift pressure from the water below ground....

Why We Crush Concrete Cube or Cylinder Samples at 28 days The crushing of concrete cubes or cylinder samples is required in a construction especially concrete structures. The reason why this is to verify the strength given in the design mix. Let say for example for a concrete column commonly it has  60 megapascals of specified strength. When you crush it, the result should be equal or more than 40 Mpa. The specified strength should be achieved at 28 days test age but sometimes we experience failure results at 28days that’s the reason we have spare cubes or cylinder samples. The spares are the alternatives that you can send at 42 days or 56 days when sample fails at 28 days test. Now, there are many questions why we crush concrete cubes at 28days. And you might be the one who’s asking. I was once who are asking about this until I came to know the reason. Read furthermore, you’ll find the answer later on this blog. You also might be asking, why we crush cubes or cy...

A Quality Engineers Guide to Concrete Cube Testing Concrete is one of the widely used building materials on planet earth. Concrete has a reliable reputation, durable and useful material. Surprisingly, people always find it challenging to take samples correctly and manage the concrete cube testing as well as the certification process. A comprehensive strength of concrete cube test provides an idea about all the characteristics of concrete. By carrying out the concrete cube test, concrete can be certified as compliant allowing clients to have confidence in its quality. Safety and reliability of concrete is the primary reason for the test. You need the following to carry out a proper concrete cube test for your concrete: • A wheelbarrow • Slump Cone • Cube moulds • Slump tray • Concrete thermometer • Mound releasing agent or oil and brush • Damp cloth • Concrete curing tank • Trowel or concrete float • A steel tape measure • A pen or marker for identifying samples • T...

Mixing of Concrete The mixing operation consists of rotation or stirring, the objective being to coat the surface the all aggregate particles with cement paste, and to blind all the ingredients of the concrete into a uniform mass; this uniformity must not be disturbed by the process of discharging from the mixer. Batch mixer The usual type of mixer is a batch mixer, which means that one batch of concrete is mixed and discharged before any more materials are put into the mixer. There are four types of batch mixer. Tilting drum mixer: A tilting drum mixer is one whose drum in which mixing take place is tilted for discharging. The drum is conical or bowl shaped with internal vanes, and the discharge is rapid and unsegregated so that these mixers are suitable for mixes of low workability and for those containing large size aggregate. Non tilting drum mixer: A non tilting drum is one in which the axis of the mixer is always horizontal, and discharge take place by inse...

EFFECTS OF HOT WEATHER ON CONCRETE Any operation of concreting done at atmospheric temperature above  40 0 C may be put under hot weather concreting. The effect of hot weather may be as follows: ACCELERATED SETTING: A higher temperature of fresh concrete results in a more rapid hydration and leads to reduced workability/ accelerated setting. This reduces the handling time of concrete. REDUCTION IN STRENGTH: Concrete mixed, placed and cured at higher temperature normally develops higher early strength than concrete produced and cured at normal temperature but at 28 days or later the strength are generally lower. INCREASED TENDENCY TO CRACK: Rapid evaporation may cause plastic shrinkage and cracking and subsequent cooling of hardened concrete would introduce tensile stresses. EFFECTS OF COLD WEATHER ON CONCRETE Any concreting operation done at a temperature below 5 0 C is termed as cold weather concreting. In the absence of special precautions, the effect of...

HOW TO CHARGE CONCRETE INGREDIENTS IN A CONCRETE MIXER? To get better efficiency, the sequence of charging the loading skip is as under 1. First place half the quantity of coarse aggregate in the skip. 2. Place half the quantity of fine aggregate over the previously placed coarse aggregate. 3. Then pour full quantity of cement (i.e. one bag of cement) over it. 4. Then deposit the remaining portion of coarse aggregate and fine aggregate over it. This prevents spilling of cement, while discharging into the drum and also this prevents the blowing away of cement in windy weather. 5. Before the loaded skip is discharged to drum, about 25 percent of the total quantity of water is introduced into the mixer drum to wet the drum and to prevent any cement sticking to the blades or at the bottom of the drum. 6. Then discharge the dry material into the drum. 7. Immediately, on discharging the dry material into the drum, the remaining 75 percent of water is added to the drum. NOTES TO REMEMB...

When we start the concreting of blinding, footing, slabs, roads and any other concrete elements. We may sometimes or commonly encounter cracks on concrete. But the question is “Why it is happening?” You might ask also “Who is to blame?” Some people would think that the supplier of concrete would probably be the source of concrete crack, but according to Mr. Crhistopher Stanley, who were our resource speaker in the seminar with the topic about “Concrete Cracking.” He said that “No concrete supplier is producing concrete that will create cracks on finished concrete.” By the way, Mr. Stanley is the Technical Director of Unibeton Readymix in UAE. We’ll, in this article I will write various classifications of concrete cracks that we usually found on the site. We will discuss one by one, the  causes  and prevention . Here are most common concrete cracks can be found on your project sites. 1. Plastic Shrinkage Crack This one we usually found on the pou...