Concrete Basics (1) Concrete Materials

Concrete is made from a mixture:

    * Cement
    * Water
    * Aggregate (gravel), coarse and fine
    * Admixture (additive) if necessary
These materials are mixed and stirred with a certain amount so easily moved, placed (poured), compressed (compact), and formed (finish), and mixtures of these materials will harden and produce strong and durable.
Amount of each ingredient is mixed (cement, water, aggregate, etc.) will affect the properties of concrete produced.
CEMENT.In powder form, and if mixed with water, will form a paste. Cement paste is used to attach and bind the aggregate among each other.

The types of cement in Indonesia, among others:- Portland cement and white- Portland cement Pozolan / Portland pozzolan cement (PPC)- Portland Cement / Ordinary Portland Cement (OPC)- Portland cement mixed- Cement MASONRY- Portland cement composites
For more stories about the cement can be read here.
Each type of cement will provide different properties on the resulting concrete. Portland cement is the most common type of cement used to make concrete mix.
Semen StorageCement if not used, must be kept properly. Cement should not be placed immediately above the ground or floor because it can cause moisture. If moist, no water vapor, so that the cement reacts with water to harden. Therefore, the holder of cement should be dry, clean, and has good air circulation.

Piles of cement also be covered with plastic sheeting or the like to provide extra protection. Do not forget, keep air circulation must be addressed.
Piles of cement is very much usually placed in special warehouses.AggregateAlso referred to as gravel, or the term handyman usually "split stone" (maksutnya opposition yo??). Anyway .. their language is a bit different, which is important can be translated into technical language.Okay .. There are two types of aggregate: coarse aggregate and fine aggregate. Coarse aggregate such as gravel or crushed rock types. While the fine aggregates are usually composed of sand and fine gravel. Sand must be real sand, not a brick or stucco sand fractions are refined.
Things about aggregates.

    * Strong and hard! Fragile and porous aggregates can reduce the quality of concrete. agg-strong
    * Resistant to extreme weather and any time. There are types of rocks that are not resistant to weather changes so easily broken. This species is not suitable to be used as concrete aggregate

*Not reactive (chemically). Aggregate should not react to the chemical constituents of cement, because it can degrade the quality of concrete.* Net. If there are layers lempur aggregate surface or soil, then the bonding between aggregate with cement will not be maximized.

 *Size gradation. Aggregate size should vary. Should not be dominated by one particular size. Gradation of this size will make the concrete more dense and to be strong 

*Spherical aggregates more easily mixed, while the aggregate angled a little more difficult but it can make concrete stronger. agg-round

Aggregate StorageAggregate should be placed in a clean from dirt like leaves, twigs, mud, and other small trash. If the aggregate is too wet (ie rain), then measure the water when mixing the concrete may be reduced.
WATER

Water serves to "dissolve" the cement that into a paste and then bind all of the greatest aggregation up to the most subtle.
Water should be clean, free of dirt or trash, and do not contain chemicals that can affect the concrete. Ground water (drill) the most widely used for mixing concrete mortar. Sea water is not recommended, because it can cause rust on iron bars. River water? Look around .. there is waste or not?

Admixture (Additive)Additives are usually added for special purposes, eg to improve the quality of concrete, accelerate the process of hardening and drying of concrete, making it easy to change the level keenceran poured, etc..
HOW process of mixing these materials?

Coarse aggregate and aggregate mixed hasul first. Then a number of cement is added and stirred into a mixture of aggregates. Add water little by little so that cement can be turned into a paste and glue the aggregate well.
   

Concrete Basics (2) Characteristics of Concrete

There are four main characteristics of concrete, namely:Workability, Cohesiveness, strength, and durability.
Concrete has three stages of the condition, namely:Plastic, Setting, and Hardening.STAGES OF CONDITION OF CONCRETE

Plastic phase. When the materials first concrete is mixed, shaped like a "batter". Soft, watery, so can poured and formed into a variety of forms. This stage is called the condition of plastic. Concrete must be in plastic condition when pouring (casting) and compaction (compaction).
The most important characteristic in this plastic condition is the workability and cohesiveness.
Our feet would sink if you tried to stand on concrete that is still in plastic condition

Setting Stage. Furthermore, the concrete will begin to harden and numb. When the concrete is no longer soft, and begins to harden, the condition is called setting. Setting occurs after compaction (compaction) and final polishing (finishing). Muddy wet concrete as placed would be easier but more difficult to do the finishing.
If we set foot on the concrete was setting, our feet will not sink, but our footprints will appear on the surface of the concrete.

Hardening stage (hardening). After going through the stage setting, the concrete begins to harden and achieve power. Characteristics present at this stage is the strength and durability (endurance).

Workability
Workability is the ability to be carried out or treated, including how concrete is easy to carry and placed everywhere, easily done, easily compacted, and easy to do the finishing.
Concrete which tends to "dry" water shortage alias of course rather difficult to set up, hard to move, even later finished to hard. If not constructed properly, concrete will not be strong and durable.
Workability of concrete can be tested by conducting slump tests. This test will be discussed in Section 3.
Anything that affects the workability?

   1. Amount of cement paste (mortar). Cement paste is a mixture of cement and water. The more cement paste mixed with coarse and fine aggregate, the greater the workabilitynya.
   2. Aggregate gradation levels. Well-graded (well-degradable), smooth surfaces and rounded shapes tend to tend to increase the workability of concrete mix.
To improve workability, can be done with

    * Adding cement paste (water + cement)
    * Use well-graded aggregate
    * Using the admixture
Warning!But avoid increased workability by adding only water, can cause menurangi strength and durability of concrete.

Strength and endurance.
A good concrete made of strong materials and durable in nature. That is, if the material forming the concrete is strong and resistant, can be secured by concrete that is produced is also more robust. Characteristics of concrete are strong and have high endurance are: solid, water-resistant (not porous), resistant to temperature change, and resistant to wear and weathering.
Strength and endurance are related. The higher the strength (quality) of concrete, the higher the durability.
Concrete is a very important to protect the steel reinforcement in the concrete core. Concrete strength is usually measured with Concrete Strength Test. About this test will also be discussed in Section 3.

Strength and endurance is determined by:

   1. Compaction. This compaction aims to eliminate air in the concrete. Of course compaction was done when the concrete is still liquid.
   2. Maintenance (Curing). Curing is the "wet" concrete has set (hard) for some time. The aim is to reduce excessive water evaporation, so water is in the concrete mixture can react optimally. The longer the curing process, the higher the durability of concrete produced.
   3. Weather. The rather warm weather can make achieving high strength concrete in the not too distant.
   4. Types of Cement. Different types of cement was also influenced by the strength and durability of concrete.
   5. Water to cement ratio, commonly referred to w / c ratio. Most water or cement can result in concrete kekuarangan become stronger and certainly not durable. W / C ratio is the ratio of water to the HEAVY WEIGHT cement. Because the weight of one liter of water equal to 1 kg, so people use more water volume ratio (in liters) of cement WEIGHT (in kg).

Concrete Basics (3) Concrete Samples To Test

There are two main testing was done with the concrete, namely:

   1. Slump Test
      Slump Test aims to show the workability or kelecakan raw terms (how muddy / watery / Muddy) a concrete mortar.
      See Part 2
   2. Compression Test Press Test or Test
      Press Test test aims to find out how much power can be achieved concrete. Test Press Test is of course done at the time the concrete has hardened.
The test must always be done with caution. Test less attention to proper procedures can give results that are not appropriate.
SAMPLINGThe first step is to take samples or samples from the batch of concrete, for example from concrete trucks or ready-mix truck. This sampling should be done as soon as possible so the truck had reached the project site. Thus, samples taken at the location, not at Batching Plant, ie places where the ready mix truck loading and mixing raw materials of concrete.
Samples can be taken in two ways:

   1. For approval may be used or not, the sample taken after 0.2 cubic meters of concrete has been poured (cast) first. So, once the concrete is poured as much as 0.2 cubic meters, then the sample was taken. If okay, the concrete may be used. If not, of course refunded.
   2. For routine checks: sample taken from each of the three sections of concrete in the truck load.

TEST slumpThe goal is to ensure that the concrete mixture is not too watery and not too hard. Slump is measured must be within range or within the limits of tolerance of the target.
Equipment

    Slump cone * standard (diamter of 100 mm, bottom diameter 200 mm, and height 300 mm)
    * Small Sekup
    * Iron rod cylinder (length 600 mm, diameter 16 mm)
    * The ruler / ruler / Ruler
    * Board slump (size 500 × 500 mm)

Procedure

    * Clean the cone. Dampen the surface with water, and place it on the board slump. Slump board must be clean, stable (not easily moved), not dusty, and not tilted.
    * Take concrete samples 

Standing on the ground (ear) that existed at the cone. Fill cone with a third of the sample. Padatkan by rodding, ie concrete poking as much as 25 times. Do it from the outer to the middle

The contents of another until it reaches 2 / 3 parts cone. Perform rodding 25 times, but only up to the top of the first layer. Not to the bottom cone

 Fill until full, do it again rodding 25 times up to the top of the second layer.

Flatten the top of the concrete was "flooded" by using an iron rod. Bersikan board slump in the vicinity of cone. Press and hold down cone, and release a foothold.

   

Lift the cone slowly. Do not let the samples move / shift

 Turn the cone, place the next sample, and place an iron rod on top of the inverted cone.

Measure the slump some point, and record the average

* If the sample fails or is outside the tolerance, then another sample should be taken, then performed slump test. If it still fails too, then the concrete may be rejected.
Compressive strength
Compressive strength test aims to determine the compressive strength of concrete that had hardened. This test is conducted in the laboratory, and certainly not at the project site (off-site). What can be done at the location (site) just make or print a concrete cylinders to be tested. Kan, sampled at the site. Not allowed to bring samples to the laboratory, then put into cylindrical molds. Cylindrical molds must be provided at the project site.
Concrete strength can be measured in units of MPa or other units such as kg/cm2. This shows the compressive strength of concrete measured at 28 days concrete age.
Sample Preparation Equipment

    * Tube / cylindrical molds (diameter 100mm x 200mm H, or a diameter of 150 mm x 300 mm H)
    * Sekup small.
    * Iron rod cylinder (diameter 16 mm, length 600 mm)
    * Steel plates as a holder

Cylinder Sample Preparation Procedure

    * Clean up mold inside surface of the cylinder and coat with oil form, so that concrete mortar does not stick on the surface of the metal from the mold.
    * Take samples of concrete mortar.

Fill half of the contents of the samples and do mold with compaction by rodding 25 times. Compaction can also be done on a vibrating table.

   Fill another sample of the concrete cylinder to mold a bit overwhelmed. Perform rodding 25 times up over the first layer

Flatten concrete overflow, spill clean-up spills and stuck to the concrete around the mold

Label. Place in a shady and dry place and let the concrete set for at least 24 hours.

Open the mold and bring to a laboratory for concrete cylinder compressive strength test.   

Basics of Concrete (4) Composition and Mixing Concrete

Concrete mortar is planned such that the resulting concrete can be easily done in a cost as low as possible, of course.
Concrete must have a high workabilitas, have higher cohesion properties when in a state of plastic (not hardened), so that the concrete produced quite strong and durable.
Mortar (mixed) concrete should consider the environment in which the concrete will stand, for example on the waterfront environment, or heavy loads, or extreme weather conditions.

Proportional
Reminder: Concrete is a mixture of cement, fine and coarse aggregate, water and additives.

Different composition of the raw materials of concrete affects the properties of concrete produced in the end. This division is usually measured in units of weight. Measurement based on volume can in fact also, and more done on a small scale construction, such as houses.

CEMENT
If the cement content is increased, the strength and durability of concrete will also increase. Cement (with water) will form a paste that will bind the aggregate ranging from the largest (coarse) to the most subtle.

WATER
Conversely, additional water will actually reduce the strength of concrete. Water is used to dissolve the cement. Water also makes mortar become cohesive, and easier to work (workable).

WATER-CEMENT RATIO
Commonly referred to w / c ratio of water to cement ratio alias. If w / c ratio is even greater, strength and durability of concrete to be reduced. In certain environments, the water-cement ratio is limited to a maximum of 0:40 to 0:50 depending on the nature of corrosive or sulphate content in that environment.

AGGREGATE










If fine aggregate is too many, then adukannya will appear "sticky", thin, "soft", such as have no power. And after compaction, the top of the mortar will tend to "empty" aka no aggregate.

Conversely, if the coarse aggregate too much, adukannya will look rough, rocky, looks brittle (fragile). This aggregate will appear on the surface after compacted.

Mixing
Concrete must be mixed and stirred well so sement, water, aggregate, and additives can be dispersed evenly in the mortar.

Concrete is usually mixed with machine. There are mixed in the field (site), there also are mixed before being taken to the field, or to say ready-mix.

For ready-mix concrete, measuring has been measured in a batch plant, then mixed and loaded into trucks. During the journey continues to play drums so that the concrete had not set in concrete in the drum. Kan strange if such taxable loss is then hardened concrete in the drum. Sometimes, in the way, it could be because the old on the street, hot weather, or run track, the temperature rise in the drum so the water evaporates. This condition is sometimes "tricked" by including a large chunk of ice blocks into the drum, so that moisture can be maintained. Hmm .. plus if a straw, we can drum truck labeled "Fresh Juice Concrete" .. : D

While the concrete was mixed in the field usually use a machine called MOLEN (something like a kind of fried banana). When mixing in the field, the aggregate first inserted into the barrel (molen), followed by a final sand and cement. Everything in certain quantities in accordance with the desired strength of concrete.

Sarankan terjemahan yang lebih baik

There was saying goes: Do not use a shovel to measure concrete mortar to molen! (Though this is often done): D
The size measure is usually expressed in units of weight, while the shovel was not able to measure weight. Do not let the mortar 1:2:3 ratio is defined as one shovel of cement, 2 shovels of sand and three shovels of gravel (aggregate). Of course the result (quality) obtained will be different. Unless there is a shovel that can be advanced as well as measuring weight of cargo.
When all ingredients (except water) are already entered, moleh rotated so that all the ingredients mixed. She's supposed to, if there is no sand visible invisible, meaning it is evenly adukannya. That's when adding water little by little.

Molen has the capacity (in volume). Mixing too full also ineffective because the mixing process will take longer. Molen should be filled to taste first, then if it is finished, the entire contents of molen poured into a container while before it was carried or cast into the formwork. When mixing concrete transported (casted), molen can work again to make the next mortar. As soon as the first mortar was poured all, molen was already finished making the second mortar, so there's no delay when molen work.

Well, for a very small scale, concrete can be mixed using a shovel. Must be done in a flat and clean (ie free of twigs, leaves, trash, and other nuisance material). Gravel, sand, and cement mixing / mixed first, then made like a mound, and at its peak made like a lake dug to retain water. If the mortar is mixed in the container sides are sealed so that water could be dammed, do not bother to make a mound, just pour water into the container. :)

In closing, we will provide tables of weight composition of cement, sand, and gravel, and water volume needed to make 1 m3 of concrete with a certain quality.
Quality Concrete Cement (kg) Sand (kg) Gravel (kg) Water (liter) w / c ratio
4.7 MPa (100 K) 247 869 999 215 0.87
8.9 MPa (125 K) 276 828 1012 215 0.78
12.2 MPa (150 K) 299 799 1017 215 0.72
5.14 MPa (175 K) 326 760 1029 215 0.66
9.16 MPa (200 K) 352 731 1031 215 0.61
3.19 MPa (225 K) 0:58 215 1047 371 698
7.21 MPa (250 K) 0:56 215 1039 384 692
24.0 MPa (275 K) 0:53 215 1026 406 684
4.26 MPa (300 K) 0:52 215 1021 413 681
8.28 MPa (325 K) 0:49 215 1006 439 670
2.31 MPa (C 350) 448 667 1000 215 0:48

Reference tables:
SNI DT - 91-0008 - 2007 The calculation mode Unit Price Concrete Work, by the Department of Public Works.

Things to Look For In a Design of Reinforced Concrete Columns

This article discusses what things to note when designing a particular structural elements of the building structure. For this first part, the elements discussed are COLUMN.

A. Analysis

   1. Type column clamping level. If using a pedestal clamp, have confirmed its foundation strong enough to resist bending moments and keep the rotation does not occur at the lower end of column.
   2. Moment of Inertia Reduction
      For the influence of cracking columns, moment of inertia of column cross section is reduced to 0.7Ig (Ig = moment of inertia of net section)
B. Load Design (Design Loads)
Must be considered in the load used for design of concrete columns is:

   1. The loading combinations.
      As a force in Test of Concrete, Steel, and Wood.
   2. Living Expenses Cumulative reduction.
      Especially for the column (and also the axial load bearing wall), live load may be reduced by using the cumulative live load reduction factor. Reference is loading Indonesia Regulation (PBI) for Building 1983
      The table is as follows:
      Total floor carried Coefficient reduction
      1 1.0
      2 1.0
      3 0.9
      4 0.8
      5 0.7
      6 0.6
      7 0.5
      8 or more 0.4

      Example How to use:
      For example there is a column that hold the fifth floor. Each floor provides live load reaction on the column amounted to 60 kN. Then the live load used for design of columns on each floor are:
      - Level 5: 1.0 x 60 = 60 kN
      - Level 4: 1.0 x (2 × 60) = 120 kN
      - Level 3: 0.9 x (3 × 60) = 162 kN
      - Level 2: 0.8 x (4 × 60) = 192 kN
      - Level 1: 0.7 x (5 × 60) = 210 kN
      So, the bottom floor is designed for live load 210 kN, it is not necessary for 5 × 60 = 300 kN.
      The basis of this reduction pengambilkan is that small possibility of a fully burdened column by live load on each floor. In the example above, one might say that it is unlikely that column receives live load 60 kN on each floor at the same time. So that the cumulative burden may be reduced.
      Note: This expense will still have to be multiplied by load factors in a combination of loading, eg 1.2D + 1.6L.
D. In Style

   1. Forces which must be taken to design in accordance with the grouping columns, including columns rocked whether or not rocking, if included short column or columns slim.
   2. The enlargement of the moment (of order unity), and P-Delta analysis (second order) should also be considered for determining the internal forces.
C. Concrete Column detailing
For detailing, the things that need to be considered include:

   1. Sectional dimension of column.
      For columns that bear the earthquake, the smallest column size can not be less than 300 mm. Comparative dimensions of the smallest column to erect lurusnya direction can not be less than 0.4. For example a square column with the smallest size of 300mm, the size of the vertical direction should not exceed lurusnya 300/0.4 = 750 mm.
   2. Reinforcement ratio shall be not less than 0:01 (1%) and should not be more than 0:08 (8%). While for the column bearing the earthquake, the ratio is 6% maksiumumnya. Sometimes in practice, reinforcement installed less than the minimum, for example 4D13 for column size 250 × 250 (ratio 0.85%). Provided that the maximum load was far below the section's capacity, okay. But if that condition is, changing the column size to 200 × 200 with 4D13 (r = 1:33%), we think it more economical. What is important with all requirements of strength and comfort are still met.
   3. Thickness of concrete cover is 40 mm. Tolerance of 10 mm for d equal to 200 mm or smaller, and tolerance to d 12 mm greater than 200 mm. d is the reduced cross-sectional size of a thick blanket. d is the distance between the outermost concrete fiber that experienced press toward the center of the tensile reinforcement. For example the column size 300 x 300 mm, thick blankets (to the point of heavy main reinforcement) is 50 mm, then d = 300-50 = 250 mm.
      Note:
      - Tolerance of 10 mm concrete cover means may be reduced as far as 10 or 12 mm due to shifting during the installation of steel reinforcement bars. But tolerance must not be intentionally done, misanya by placing "concrete knowing" for 30-mm-thick blanket.
      - Mortar plastering and finishing the concrete cover is not included, because the mortar and finishing at any time can easily be rusted either intentional or unintentional.
   4. Pipe, channel, or a cover which is not harmful to concrete (not reactive) may be planted in the field, provided that the extent of not more than 4% of net cross-sectional area of the column, and the pipe / channel / sheath should be planted in the concrete core (inside diameter of a circle / ties / begel), not in concrete cover.
      Aluminum pipe should not be planted, unless given a protective coating. Aluminum can react with the concrete and steel reinforcement.
5. Spaces (clearance) between bars along the side of the transverse reinforcement must not exceed 150 mm.kolom_14036_image0056. Sengkang / ties / begel is an important element in the column, especially at the regional meeting of the beam-column in the resist earthquake loads. Fitting stirrup should really comply with the requirements of SNI.In addition to shear forces, transverse reinforcement is also useful for holding / megikat main reinforcement and concrete core does not "jump" when receiving a very large axial forces when an earthquake occurs, so that the column can develop resistance to the maximum limit (eg reinforced concrete began to melt or the voltage reaches 0.85 fc ')# Transfer the axial load on the structure of a quality different floors.In high-rise building, sometimes we design the columns and floor plates with different concrete quality. For example slab using fc'25 MPa and MPa fc'40 column. At the time of execution (casting floor), the column that intersect (intersection) with a floor would be casted according to the quality of the concrete slab (25 MPa). This intersection region to be checked against the axial load on it. Not uncommon in this area needed additional reinforcement to mengakomodiasi strength due to different concrete quality.