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For Hot Weather Concreting requirements, see Section 7.
Standing water shall be removed prior to placement of concrete. Stairs, steps, ramps, and walks shall be finished with a broom finish. Vendors shall supply datasheet including third party test reports.
Outdoor sidewalks are exempted from this requirement. Commentary Notes: APCS shall not be used where soil is contaminated with hydrocarbons and compatibility test shall be conducted when concrete surface is cured with acrylic based curing compound. Non-structural concrete such as lean concrete or thrust anchor blocks without reinforcement does not require coating.
Concrete envelopes for underground ducts and cover slabs for directburied cables can be colored by adding 6 kilograms of coloring oxide powder per cubic meter of concrete unless otherwise specified in contract documents. The evaluation shall include identification of marine organisms including rock boring mollusks and sponges that would pose a threat to the concrete structure and its integrity.
Specific susceptibility of the concrete structure to attack by boring organisms in the Arabian Gulf has been associated with the use of calcareous aggregates where the main constituent of the aggregate is CaCo3 in the concrete. Commentary Notes: Marine structure — any facility that is in contact with sea water.
ACI certification pro- grams identity craftsmen, technicians and inspectors, who have demonstrated their qualifications.
The follow- ing programs are administered by AC! Ifnot, suggested guide specifications are available on request from the ACI Certification Department. To assist in the effort for accuracy and clarity, the Technical Activities Committee solicits the help of in viduals using ACI reports and standards in identifying and eliminating problems that may be associated with their use.
Users who have suggestions for the improvement of ACI documents are requested to contact the ACI Engineering Department in writing, with the following information: 1. Title and number of the document containing the problem and specific section in the document; 2.
Concise description of the problem; 3. More careful examination may reveal that a considerable proportion of the cement is in the upper layers of the concrete, possibly appearing as a thick laitance on the top surface.
The significance of a lack of full compaction on concrete strength is well known Figure 1.
Established practice is to specify slump values of mm. These values offer a useful guide for trial mixes but, as concretes with a given slump can have varying flow properties, the ability to self-compact needs to be assessed by practical trials. Experience has shown that concrete with relatively low cement content has better abrasion resistance.
These conflicting performance requirements have led to the use of admixtures and cement replacement materials. Non-dispersible concretes can be produced with varying degrees of cohesion and washout resistance. The turbidity of the water is measured using standard light transmittance apparatus. By calibration using standard known dispersions of cement in water, the amount of washout occurring as a result of the concrete falling through the water can be determined Figure 1.
Ordinary Portland cement was dispersed in water prescribed period. This is a more stringent test but produces similar comparative results.
A measured volume of water is poured down the channel and depending on the segregation resistance of the concrete, cement is washed out. However, by standardizing the volume and speed of water flow, and collecting it at the downstream end of the channel, the transmittance of the effluent can be measured as above, thus enabling comparative performance to be judged on a numerical basis. The sample is hauled to the surface slowly 0.
A total of five drops has been accepted as standard. While the rate of fall of the basket and concrete is relatively faster than the free-fall speed of concrete alone, the protective effect of the mesh of the basket mitigates against this. The results of the test are repeatable, enabling good comparisons between different concretes to be made.
It is generally thought to relate well to practical conditions of free fall from a pump delivery hose through m of water. The results are shown in Figure 1. The upper hopper is filled loosely with concrete, then a trap door is opened allowing the concrete to drop into the lower hopper.
The concrete is then allowed to fall over a smooth steel cone, in air or through water, and scatter on to two concentric wooden discs. The weights of fresh concrete and sieved and oven-dried coarse aggregates which were collected from the two discs are used to determine the separation index SI.
The standard slump and flow tests BS Parts and are appropriate but it is interesting to note that where cellulose ether has been used to produce non-dispersible concrete the slump value gradually increases with time up to 2 min after removal of the conical mould , and the diameter of the concrete continues to increase following the flow table test.
It is common practice to allow sufficient time for the concrete shape to stabilize prior to taking a reading. Figure 1. The US Army Corps of Engineers' standard test method, CRD-C, can also be used for determining the flow of concrete intended to be placed underwater using a tremie.
Of more direct practical value is the speed of setting. Typical values obtained using the Proctor Probe apparatus are given in Figure 1.
The rate of gain of strength can be determined by casting multiple specimens and testing at intervals over several weeks. Once again comparison with control specimen results enables the influence of the admixture on hydration to be assessed.
Alternatively, the modulus of elasticity can be determined electrodynamically. This has the advantage of using the same specimens at each interval of time. Much ingenuity has been used to develop such tests. Production of cubes by dropping concrete into moulds placed in water tanks is the most common approach but does not readily simulate practical conditions. A better approach is to produce mm diameter castings in moulds which include simulated reinforcement.
These need to be sufficiently large to enable mm diameter cores to be cut to provide the test specimens. The long-term durability of concrete containing the normal range of admixtures is well established. Less direct evidence is available for non-dispersible admixtures, particularly in terms of synergistic effects. However, the addition of micro silica to enhance the strength and durability of concrete has become established practice.
There is over 15 years of evidence of the durability of non-dispersible concretes containing cellulose ether, and acrylic latex has been used to enhance the properties of hydraulic cement concretes at much higher proportions than are used in non-dispersible concretes for well over 10 years. The long-term durability is not therefore likely to be reduced by the use of these admixtures and, in view of the more reliable quality achieved, durability is likely to be enhanced.
Unless first-hand experience of the actual placing conditions is available, it is good practice to cast trial sections of projects under the prevailing conditions.
The costs involved are justified in view of the financial and safety implications of failure. References 1 Techenne, D. Staynes , International Congress Polymers in Concrete.
Brighton University. International Congress Polymers in Concrete. Dikeou and Fowler ACI.
Marine Concrete '86—The Concrete Society. Secondary functions are to give shape and texture to the exposed faces of the structure. Under water this changes.
Whilst its prime function is still to support the concrete, texture is not important but the formwork must provide protection against washout of cement and scour due to movement of water. Additionally, liaison between surface and bottom will be complicated by difficulties in communication and loss of orientation.
Because of this the practicality of each operation required in the preparation of and in fixing and striking formwork must be analysed in detail. Although there have been major advances in equipment, tools and underwater breathing apparatus, there is little that is essentially new in underwater formwork.
The Victorian engineers faced some of their greatest challenges in the construction of harbour works and many of the techniques devised or developed by them to facilitate construction under water are still in use today. These include mass bag work, reusable form work, precast blockwork and slab work, precast concrete caissons, tremie and under water skips, as well as mammoth temporary works such as the travelling shield described by Kinipple in a paper on concrete work underwater given to the Institution of Civil Engineers in The introduction of iron and steam-powered mechanical plant and later the development of diving equipment and techniques enabled construction to move into deeper, more exposed water.