Make an Order Call +254 (0) 722 632289,(0) 733 632145

Nairobi Sales Office

Bamburi Special Products Ltd, Sales Office
Kitui Road, off Kampala road, Industrial Area
P.O Box 30669, Nairobi
Mobile: +254 (0) 722 632289, (0) 733 632145
Email:bsp.info@lafargeholcim.com

BSP Plant

BSP Plant, Athi River
Off Namanga road, Athi River
P.O Box 30669 -00100, Nairobi
Mobile: +254 (0) 722 632289,(0) 733 632245
Email: bsp.info@lafargeholcim.com

Mombasa contacts

Bamburi special products ltd
Felix Mandel avenue,off -Malindi road, Bamburi.
P.O Box 10668-80101, Mombasa
Office Mobile;+254-722632289/733632145
Email; bsp.info@lafargeholcim.com

Please Select Your Question Category

Demystifying Facts About Ready-Mix Concrete

Fact: There are other, more effective ways to increase concrete slump besides adding more water.Adding excessive amounts of water at the jobsite will increase slump, but will also reduce strength significantly. The added water dilutes the paste and increases the water-to-cementitious materials ratio (w/cm). Too much water can increase drying shrinkage, and lead to other service-related problems.Many specifications forbid any onsite addition of water. Even so, there are other ways to increase the slump and workability of concrete. Aggregate gradation and the maximum size of the aggregate both greatly influence cement and water requirements, which affect mix workability. Water reducers and superplasticizers can also be used to increase the slump while maintaining the water-to-cement ratio. And air-entrainment can increase workability. Adding water to a mix that contains chemical admixtures will change the properties of the mix and can cause excessive slump loss, inconsistent setting, and changes in air content.
Fact: Mixes should be specified based on performance requirements, not just cement content.Some in the concrete business still call out concrete mixes based on the number of bags of cement (a 6-bag mix, or a 7-bag mix), but bag counts don't accurately describe the desired properties of the concrete. But how much cement is necessary to get high-quality concrete? It depends on the intended use.To maintain economy and avoid adverse effects on workability, shrinkage, and internal temperature rise, high cement contents should be avoided. Minimum cement contents are often specified to improve durability, finish ability, wear resistance, or appearance (of vertical surfaces). The most important property of concrete starts with the water-to-cementations materials ratio.
Fact:Even the densest concrete is somewhat porous.Water and other substances in liquid or vapor form can pass through concrete. Depending on the overall porosity of the concrete, that can take anywhere from a few minutes to a few months.Concrete can be made less permeable and more watertight by using mix designs with a low w/cm, well-graded aggregate, chemical admixtures such as superplasticizers, and supplementary cementing materials such as silica fume or fly ash. Surface treatments, like sealers and membranes, may also be considered.
Fact:Compressive strength alone does not determine the concrete's durability.Although compressive strength is an important characteristic of concrete, other qualities can be even more important for concrete durability in harsh environments.In general, the principal causes for deterioration in concrete are corrosion of reinforcing steel, exposure to freeze-thaw cycles, alkali-silica reaction, and sulfate attack. Reducing permeability is the key to durability.
Fact:Calcium chloride is an accelerator only and not antifreeze.Accelerators speed up the rate of hydration and strength development of concrete at early ages. Fresh concrete, however, still needs protection from freezing at least until the concrete reaches a minimum strength of 500 psi. Without that initial protection, concrete that freezes will have significantly reduced strength.To avoid cold weather placement problems, make sure the concrete is properly protected and that its temperature is maintained, following the guidance provided in ACI 306 "Cold Weather Concreting."
Fact:Concrete will change in volume while setting, hardening, and drying.Curling of slab edges is caused by differences in the moisture content and temperature of the top and bottom of the slab. The edges of slabs at the joints tend to curl upward when the top surface of the slab is drier or cooler than the bottom surface.A "reverse curl" occurs when the top surface is wetter or warmer than the bottom. Curling can be reduced by using techniques that minimize shrinkage differentials and the temperature and moisture-related volume changes that cause them.
Fact:Structural reinforcement does not prevent concrete from cracking due to volume change.Concrete that is restrained from moving during volume changes may crack, since concrete is weak in tension. Many times, reinforcing steel actually causes the restraint.Structural reinforcement does not prevent cracking, but rather it holds the crack faces together. When concrete cracks, the tensile stress is transferred from the concrete to the steel, which is what allows reinforced concrete to withstand higher tensile loads than concrete alone.
Fact:Concrete needs water to continue to hydrate and gain strength.
Concrete does not harden by drying out. As long as there is sufficient moisture and favorable temperatures, the hydration of concrete will continue for quite some time. When fresh concrete does dry out (usually below about 80% relative humidity), hydration stops. If the temperature of fresh concrete approaches freezing (below 40[degrees]), hydration slows dramatically.The need to provide moisture and an adequate temperature immediately after placement is why we cure concrete.The longer you cure concrete, the stronger and more durable it will become.
Michelle L. Wilson is program manager and David F. Ey is concrete engineer, both in the Education and Product Development department at the Portland Cement Association, Skokie, Ill.

FAQs on Ready Mix Concrete

Apparent ready mixed concrete shortages are caused by:

1. Miscalculation of form volume or slab thickness when actual dimensions exceed the assumed dimensions by even a fraction.
2. Deflection or distortion of the formwork.
3. Irregular subgrade and its settlement.
4. Smaller quantities wasted or used in incidental works for large pours.

 To ensure sufficient supply of ready mixed concrete: 

1. Measure formwork accurately and order sufficient quantity to finish the job.
2. For large pours, include an allowance of about 2% over planned dimensions to account for wastage, potential increased thickness, etc.
3. Towards the end of large pours, carefully measure the remaining volume and confirm the closing quantity to the ready mixed concrete supplier.

NO! Restrain masons at the site. Do not force Transit Mixer Operators to add water to ready mixed concrete. Consequences of such actions can be severe. Properly designed ready mixed concrete contains optimum water.Inform the ready mixed concrete supplier if workability (slump) of ready mixed concrete is not as expected. If required, dosing of admixtures along with a small quantity of water would be done by the ready mixed concrete supplier´s technical personnel.
Ready mixed concrete mixes are supplied only after exhaustive laboratory and plant trials.To ensure consistent quality, incoming raw materials are regularly tested. Sampling and testing of ready mixed concrete is done everyday as per Codal stipulations.At our Bamburi Ready Mix Concrete, we invite you to visit our laboratories to witness the process.
Bamburi Ready Mix Concrete can deliver a minimum load size of 4 cubic meter.
Depending on the workability, the ready mixed concrete might be usable for up to 3 hours.
International Standards specify that ready mixed concrete must be discharged from the transit mixer truck within 2 hours of the time of loading. It is also mandatory to make arrangements at site to ensure that full load of ready mixed concrete is discharged within 30 minutes of arrival on site.
 

FAQ on Transit Mixer and Boom Pumps

When the ready mixed concrete is transported to the construction site, the ready mixed concrete is pushed deeper into the drum attached to the back of the truck with the help of a spiral blade fitted within the drum. This is achieved by rotating the drum in one direction. This process is known as charging the transit mixer.At the construction site, the drum is rotated in the other direction, which forces the ready mixed concrete out of the drum. This process is known as discharging. The ready mixed concrete may be discharged directly into chutes, pumps or on to conveyor belts.
The transit mixers are about 9 m long, 2.5 m wide and 3.8 m high
Pumps are designed to facilitate pumping of ready mixed concrete through the pipeline under high hydraulic pressure.When ready mixed concrete is pushed through the pipeline, it is separated from pipe line wall by a lubricating layer of cement, water and fine aggregates. Ready mixed concrete should have enough cohesiveness and workability for the mix to move easily through pipeline, bends, reducers and hoses.

Why Concrete cracks

When placed concrete typically contains more water than is required for hydration of the cement. As the concrete hardens and starts to lose the excess water, shrinkage begins. If the concrete is unrestrained, no cracks will develop. But it is virtually impossible to support a structure of any appreciable size without some restraint.The cracking phenomenon is complex and depends upon a number of things; rate and amount of drying, drying shrinkage, tensile strength, tensile strain, creep, elasticity, degree of restraint, and other factors.While most types of cracking do not affect structural stability or durability, all cracks are unsightly and in extreme cases cracking can reduce the use and serviceability of the structure. For this reason, cracking should be kept to a minimum.In the laboratory, drying shrinkage tests are the most easily and most frequently performed tests in relation to shrinkage/cracking problems. However, there is sometimes too much emphasis on the drying shrinkage of hardened concrete as the criterion of susceptibility to cracking.Drying shrinkage alone is influenced by many factors - water/cement ratio; amount, fineness and composition of cement; mineral composition, stiffness, shape, surface texture, and grading of the aggregate; characteristics and amount of any admixture; size and shape of the concrete mass; and conditions of humidity and temperature.Preventative measures at the time of placing and curing remain the best means of minimizing cracking.

In most cases where cracks appear in concrete the crack can be identified and the cause of cracking established. An extensive survey carried out revealed that concrete cracking can be attributed to the following:

Construction and supervision problems - approx. 36%.

Design defects - approx. 27%.

Ambient conditions (temperature, humidity, etc.) - approx. 21%.

Quality of materials - approx 17%.


In addition, all cracks can be grouped into two broad categories:

Cracks occurring before and during hardening.

Cracks occurring after hardening of concrete.

Shrinkage cracks:

Avoid by cutting contraction joints along dotted lines.

Shrinkage cracks caused by stress concentration at corners:

Prevent by placing expansion joint along dotted line, or by using reinforcing steel.

Settlement cracks caused by movement of sub-grade or footings.

Cracks due to heaving under the slab through poor drainage of sub-grade.

Expansion cracks:

Prevent by placing expansion joints at dotted lines.

Shrinkage cracks in feathered sections:

Narrow feathered sections should be avoided.Plastic shrinkage cracks:

Due to quick loss of water to dry sub-grade or to the atmosphere.

Shrinkage cracks at door or window corners:

Avoid by use of reinforcing steel or (in solid concrete walls) by careful placement of low-slump concrete.

Plastic shrinkage cracks occur when wind velocity, low relative humidity, high ambient temperature, or a combination of all three, cause water to evaporate from a concrete surface faster than it can be replaced by bleeding to the surface. The rapid evaporation which causes this cracking can be checked by windbreaks, shading and surface treatments.Vertical cracks may be caused by the settlement of concrete around reinforcing bars. Such cracks occur when the concrete near the surface takes a partial set while the rest of the concrete is still able to settle. Cracking of this type can be identified by a pattern which follows reinforcement. Thus cracks can often be prevented by revibration of concrete. Sloping cracks sometimes appear when coarse aggregate particles near the surface form a skeleton in which cement paste can settle and separate. Once again, vibration and revibration will reduce or prevent cracking.Relatively small movements of formwork in the early stages of hardening will cause cracks. Swelling or bulging of timber, springing of nails, clumsy or excessive use of vibrators are the common causes of form movement resulting in irregular cracks.Wide cracks, sometimes extending through the slab, occur when sub-grade subsides before concrete has developed strength. This may occur because the sub-grade is not level and well compacted, or is muddy, or is unstable for any other reason.
This category covers the performance of concrete whose shape can no longer be altered without damage It includes cracks caused by drying shrinkage, as well as those which result from the temperature movements which take place in all materials exposed to the elements. Unless the structure concerned permits movements of its members without development of excessive stresses, extensive cracking often may occur.Crazing cracks after hardening can result from excessive floating which tends to draw water and cement to the surface, which then comprises weak concrete subject to high shrinkage stresses. More often, they result from poor curing. Other cracks which occur after hardening can be caused by lack of adequate reinforcement at corners, insufficient depth of concrete over bends in reinforcement, nesting of reinforcing steel in concrete, lack of expansion and contraction joints.
Shrinkage cracks cannot always be prevented, but they can be controlled by making planes of weakness to establish the direction of cracking when contraction occurs. This is done by cutting slots one third the thickness of the slabs, and is done as soon as the concrete is hard enough to resist damage by the saw. Cracking, if it occurs, will then occur neatly beneath the line of the slot. (If the cutting is left much later than the point of time mentioned, surface cracks may suddenly appear, veering off the line of sawing).The contraction slots should be cut at logical points of stress in paths, at ½ to 2 metre intervals (lightweight paths can be scored with a double edger); in driveways or large floors, at 5 to 7 metre intervals. Where the floor is divided into bays by columns, the joints may be placed from column to column for better appearance (see illustration). However, they should not be more than 7 metres apart unless slabs contain substantial steel reinforcement. Expansion joints, or isolation joints, usually consist of pre-moulded tar material 10mm thick, as deep as the slab, and as long as the slab. They should be placed where paths or driveways meet, and where slabs meet a column base, wall, or any other mass which will resist expansion in that direction (see illustration).
To enable it to be poured and worked, nearly all concrete contains more water than is needed for hydration of the cement. The addition of water to ready mixed concrete increases the likelihood of segregation and excessive bleeding, which will cause the concrete surface to be porous, weak, and prone to crack.On the other hand, during curing, too-rapid evaporation of water from the surface will also make the surface prone to crack, and ponding, fog-spraying, or water-retaining covers should be applied continuously throughout the process. The supervisor's perennial problem is to make his men understand that too much water at the placing stage is as harmful as too little at the curing stage.
The majority of cracks occur within 2-3 days after concrete has been placed. These are preventive measures which will minimise cracking in that period:

See that sub-grade is well-compacted.

Check that form work is firm.

Ensure that sub-grade and form work are moist before pouring.

Do not add water to ready-mixed concrete in placing.

Compact low-slump mixes well.

Cut sufficient contraction joints to allow for shrinkage.

Provide expansion joints where necessary.

Start curing as soon as possible.

Maintain proper curing for an adequate period.
By the use of the procedures in this publication and by exercising proper care you will obtain the best performance from your Bamburi concrete.
Bamburi Special Products operates an accredited laboratory with trained technical staff who are available to answer any technical enquiries you may have and assist in designing concrete mixes specifically for your needs.

Bamburiblox and Wet Products

50Pcs
 
There is no physical difference. The difference is in the compressive strength of the particular block. Heavy duty block has a compressive strength of 49 N/mm2. Medium duty block has a compressive strength 35 N/mm2.
10 m2

One stack of 50 mm blocks weighs 1.1 tons

One stack of 60 mm blocks weighs 1.3 tons

One stack of 80 mm blocks weighs 1.8 tons

0.9 m long

We are the pioneers in the development of concrete paving blocks in Kenya. We also provide a commercial supply of ready mix concrete to meet a wide spectrum of clients in the construction industry.

Sustainability

Our continued success is dependent on the quality of relations we have with all our stakeholders. Deliberate efforts are made to nurture strong relationships that contribute to socio-economic development that is mutually beneficial and partnering to promote the well-being and prosperity of communities we operate in.

Contact Us

Kitui Road, off Kampala road, Industrial Area

P.O Box 30669-00100, Nairobi. Kenya

Make an Order Call +254 (0) 722 632289,(0) 733 632145

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