QAQC in Construction

There are different types of building blocks used in Pakistan. Before discussing their prices and types. Let’s talk about their composition and history. HISTORY In contemporary construction, cement and concrete blocks are important and versatile building materials. They are mainly built for construction purposes. They are used in multiple  applications such as, for the construction of fountains, walls, floors, and walkways. Cement and concrete blocks have been in use for a very long time. The Romans used to build their colosseum and iconic structures with blocks. In the present time, blocks are used for modern constructions. Now, they are used for the fabrication of housing societies, commercial and industrial buildings. COMPOSITION Concrete blocks are composed of a mixture of cement and aggregates. Cement holds the other materials together. Sand and gravel gives strength and durability to the block. On the other hand, cement blocks are similar to concrete blocks, although they are...

1. Drying Shrinkage Concrete by nature is a porous material. This means that when it is curing, the water in the concrete takes up space. As concrete hardens, it loses its moisture through evaporation resulting in empty capillary pores and a slightly smaller shape. This process is known as drying shrinkage. Since concrete is very rigid, this shrinkage causes an increase in tensile stress, which may lead to, cracking, internal warping, or external deflection. Concrete cracks when the drying shrinkage stresses exceed the tensile strength of the concrete. The spacing and size of cracks depend on the amount of shrinkage, degree of restraint, and amount and type of reinforcement. Drying shrinkage is the number one reason for cracks in concrete. 2. Lack of / improper use of control joints Control joints are most commonly installed in slab-on-grade concrete that is used in places such as driveways, pavements, house slabs, basement floors, and industrial spaces.  Control joints are general...

Concrete mix design is a method of calculating the right proportions of cement, sand, and aggregates for concrete to achieve target strength in structures. The Concrete mix design Concrete Mix = Cement:Sand:Aggregates. There are two Methods Volume Batching Weigh Batching For a mix design of concrete, we have to follow various steps, calculations, and laboratory testing to find the right mix proportions. M20 (1 cement :1.5 sand :3 stone/brick aggregate). To determine the proportions you have to perform mix design, you have to find out the Specific Gravity  of cement, CA, FA, and water-cement ratio, type of exposure, Maximum size of aggregate, etc. Once the W/C ratio is determined use 186 kg water (for 20mm CA) to find out the qty. of cement per cum of concrete. Then determine the qty. of FA and CA with the help of the formula given in IS:10262-1982, and then divide all the ingredients by cement, then you will get the proportion similar to you mentioned which are in kg. Or you can fo...

Cementitious Materials in Concrete Define and classify various cementitious materials; Understand the effects of cement fineness on water demand and concrete strength properties Recognize the importance of controlling the heat of hydration in concrete; and Identify the types of blended cement and the performance benefits of each for certain applications. List the standard tests used to determine properties of hydraulic cement; Understand why the water demand changes when using fly ash and pozzolans; Discuss the differences in strength gain for concretes with and without pozzolan replacement of cement; and Recognize the advantages of using ground granulated blast furnace slag and silica fume in concrete. Explain the synergistic effects of using multiple Supplementary Cementitious Materials (SCMs) in a concrete mixture. Recall methodologies for evaluating ternary and quaternary blends of materials for use in concrete. Describe considerations for construction using ternary and quaternary ...

  Design Mix: This test helps in determining the suitable ingredients of concrete and determining their relative amounts with the objective of producing concrete of the required strength, durability, and workability as economical as possible is termed as concrete mix design. It involves studying properties of Aggregate, Cement, Water & Admixture (if any), and is used to determine the proper Concrete Mix Design. Ref: ACI 211.1 Ultrasonic Survey: Ultrasonic concrete testing is based on the pulse velocity method to provide information on the uniformity of concrete, cavities, cracks, and defects. The pulse velocity in a material is directly proportional to its density and its elastic properties which in turn depends on the compressive strength and the quality of the concrete. It is, therefore, feasible to obtain information about the properties of components by sonic investigations. Test Method: IS 13311 (Part 1) Chloride Content: Measuring the calcium chloride content of...

The physical and mechanical properties of the interlocking concrete blocks shall conform to the following requirements.  A. Bulk Density (min. 48 hrs. immersion): Average > 2.375 T/m3 Minimum = 2.330 T/m3 9  B. Bulk/Apparent Density Ratio (min. 48 hrs. immersion) Average > 0.88 Minimum = 0.87  C. Water Absorption (min. 48 hrs. immersion, tested according to ASTM C140) Maximum = 3% for aggressive exposure zones1 4.5% for less aggressive exposure zones2  D. Compressive Strength (min. 48 hrs. Immersion tested according to BS 6717:1993) Average ≥ 55 Mpa for aggressive exposure zones, and 49 for less aggressive exposure zones Minimum = 47 Mpa for aggressive exposure zones, and 44 for less aggressive exposure zones  E. Abrasion Resistance (for vehicular areas only, tested as per ASTM C418) Average thickness loss < 3 mm Maximum volume loss = 150 mm3 per 500 mm2 Or comply with BS EN 1338 (maximum volume loss 20,000 mm3 per 5,000 mm2  F. Flexural Stren...

Major factor should be considered when placing the concrete on-site delivered from the batching plant/Mixing plant, Many and varied below:- Ambient temperature (The Weather During the Casting Time) Specification for the Mix Design Sub-grade Condition Type of Installation (Lean, Structure, Column, Beam, etc.) Form Securement Type of reinforcement Sufficient personnel capable of placing the concrete. Pouring Rate Height of Free Fall of Concrete must not be more than 1.2 m. Avoid Cold Joints

Common Concrete Pouring Issues 1. AIR LOSS: During concrete pouring, air loss can cause problems. Several factors lead to this, such as long vertical drops, high initial slump, increase in pressure, or drop in exit. For every 1% decrease in air, strength decreases by 4-5%. You can fix this problem by adding a gate at the end of the pump line for restriction. It also helps to keep the boom in an upward or horizontal position as much as possible. If this can’t be done you can put multiple 90 degree elbows into the line to slow down concrete, minimizing the straight dropout. 2. BUG HOLES: Bug holes are evident by a small void on the outside of formed concrete surfaces. These come from poor application of form release agents to form-work or completely forgoing their use entirely. It can also come from stiff or sticky concrete mixtures. This can also be caused by poorly placed internal concrete vibrators. To solve the problem of bug holes, make sure release agents are applied...