Ready-Mix Concrete Vs. Concrete Made On SiteNovember 1, 2018
Below is a list of guidelines to justify your choice and obtain a remarkable final economy with ready-mix concrete. Given those certain structural elements of a work, such as beams, castles and floors, etc., that occupy small volumes, it is common that many times, and at the request of the construction manager, they are required to manufacture in situ. But when a homogeneous concrete of controlled quality is needed that has the backing of the technical assistance of the specialized supplier,
The most outstanding advantage in the use of ready-mixed concrete is the guarantee of its production in terms of the mechanical properties of the material, endorsed not only by a rigorous control by continuous tests carried out on the final product but also different controls are carried out. Components, through a statistical treatment of them, and the permanent training of the personnel involved in these tasks.
Control of components
Every supplier of ready-mix concrete before deciding the use of a source of stone aggregates must determine its various physical characteristics, such as specific weight, absorption, humidity, and granulometric composition. After being accepted, periodic tests must be continued to reassess that these same characteristics will last when receiving new materials and ensuring the homogeneity of the concrete throughout the manufacturing process. Its storage must be carried out with adequate methods so that the indicated properties are not modified.
Cement is also controlled by standardized tests related to fineness, compressive strength, setting times, etc., and less often chemical analysis is carried out since, at present, it is a material duly controlled by the industry of cement and that is backed by a quality protocol. In the case that it is decided to use chemical additives, tests are carried out in the plant laboratories, which allows making the best choice and dosage of them according to the mixture of cement and aggregates that will be used.
Concrete and useful life
Concrete is a material that has the particularity that it can be made anywhere and in any way, but it must be clearly understood that the way of execution, the control of materials, and their placement and cured, the future quality of the concrete structure depends on its entire useful life. Concrete is one of the few materials or products that are not storable; therefore, it cannot be produced and maintained to check its quality before being used in the work (with the exception of prefabricated elements).
This requires extreme care in the selection of raw materials before their use and in the processing criteria.
Dosage by volume
If one or two bags of cement, stone aggregates, sand and some buckets with water are mixed with a shovel or a mixer, concrete is obtained. This material prepared on site can only require a resistance according to minor structures with low compressive strengths. But if we talk about complex structures and with special requirements we must in some waypoint to an efficient control of quality, resistance, and durability. It is often believed that certain cement consumption per cubic meter of concrete ensures a compressive strength specified in the project. But this, generally,
Dosage by weight
The premixed concrete dosage is always carried out by weight in the premixing plants. The operator of the plant receives from the laboratory personnel the final dosages with which he must work, whose contents are within the limits established by the regulations in force, determining the humidity of the materials and thus guaranteeing an adequate proportion of coarse aggregate and fine, which will result in a more homogeneous concrete, cohesive in a plastic state and more durable in a hardened state. The balances of the clock and the cells of load that are used as a system of weighing of the dosing plants are reviewed and calibrated periodically, always being a record of said procedure. The quantities used in each delivery are recorded in the load part issued by the automation system, in order to check that the quantities indicated in the dosages were actually used and to carry out the stock control of the inventories.
One of the most remarkable aspects of the production of ready-mix concrete is the human element. The pre-mixer companies pay special attention to the training and experience of the personnel in charge of managing the plant, usually having many years of experience in the field. Thus, the person in charge knows at first glance the workability and cohesion of the concrete that is being produced, and together with the person in charge of the plant laboratory, they make the appropriate adjustments, if necessary, so as not to alter the cement content and produce concrete. Quality. The quality control on the finished product is carried out in a rigorous way by means of samplings in the premixing plant or in the work itself, determining first the slump, the workability, the cohesion, d the continuous elaboration of test cylinders to determine the resistance to compression of the concrete. With the results obtained from these determinations, a statistical record is made to verify the uniformity and compliance with the rules in force for ready-mix concrete (NMX or ASTM Standards).
a) The location of the work, accessibility, and relationship with the surrounding urban environment.
b) The concrete classes and the purpose of the structures.
c) Technical requirements.
e) Total amount to be produced.
f) Type and size of each structural element.
g) Availability of ready-mix concrete in the local area.
i) Type of contract, design, and construction, characteristics of the client or constructor.
In a next stage, a decision must be made between the two methods, premixed or done on site, after a careful evaluation of the commercial and technical options, together: with a practical and efficient program of tasks. Concrete Batching machine is the best option for all construction company.
If the ready-mix concrete option is considered, a cost analysis must be performed. Depending on the contract, it must be taken into account if the concrete is required, for example, outside normal working hours, which will require including additional costs, along with the charges for waiting and loading times. In the case of concrete made in situ, the preparation is more onerous and becomes more complex. Compared to the ready-mix concrete option, a similar amount of material still needs to be transported by road. However, the number of trips can be substantially reduced if the appropriate material complies with the respective standards and can be locally available.
Problems that can occur in the preparation of concrete on site
a) Reduction of durability.
c) Variations of the resistance to compression or bending.
d) Segregation of the component materials.
e) Lack of continuity in the structural element.
f) Significant contractions.
g) Increase in permeability.
h) Increase in bleeding.
i) The risk in the stability of the structure.
j) Reduction of the adhesion capacity with the reinforcing steel.
k) Reduction or variation of the modulus of elasticity.