Mix, concrete

Concrete additives Concrete and masonry Concrete mixes Concretes... 

Water-Repellent. Three techniques used for water repeUency are modification of cement by the addition of waterproofers, use of repellent additives to the concrete mix, and surface treatment of concrete stmctures with repellents. The modification of portland cement by intergrinding with stearate salts or other water-repellent material can reduce the water permeabiUty of mortar. Considerable controversy exists, however, as to whether these cements produce concrete that is superior to carefully mixed concrete without such additives (79). 

Water-Reducing Agents and Superplasticizers. Common admixtures that improve fluidity of concrete mixes are often used in high strength concrete. These admixtures make possible the incorporation of siUca fume while maintaining necessary workabiUty. Three principal types of... 

J. L. Goodrich, "Asphalt and Polymer-Modified Asphalt Properties Related to the Performance of Asphalt Concrete Mixes," Msphalt Paving... 

This relies on the integrity of the concrete construction itself with reference to design (crack control, joint spacing and detailing, concrete mix) and skilled workmanship and supervision. 

Schutt reported that the coke breeze specification and conditions in which the mix is prepared are important factors in determining the optimum operation of the conductive cement mix, whilst further details on the coke breeze asphalt mix composition are given by AndersonConductive concrete mixes, with a polymer binder have also been developed as an anode system specifically for reinforced concrete cathodic protection systems . 

The surface of concrete may be subjected to cycles of wetting and drying during normal service life. This process is a durability concern as harmful ions such as chlorides or sulfates can easily penetrate with the adsorbed water and there is the potential for saturation prior to freezing. Measuring the rate of water penetration into a dry concrete surface is thus important to the quality control of concrete mixes - hopefully yielding a durable product. 

Table 12.2 shows a typical concrete mix. The exact amounts may vary by as much as 50% depending on the intended use and preference of the concrete maker. 

The way in which the four types of water-reducing admixtures discussed so far affect the strength gain characteristics of concrete containing them is shown in Fig. 1.2. The four concrete mixes have been designed to have approximately the same 28-day compressive strength, i.e. the admixture-containing mixes would contain approximately 10% less cement than the control mixes. 

When a normal, accelerating, or retarding water-reducing admixture is utilized to increase the workability of a concrete mix by direct addition, it would be reasonable to assume that the extent of the effect would be markedly affected by changes in mix design parameters such as cement content, aggregate size, shape and grading, and the water-cement ratio. A study of many hundreds of results, however, indicates that this is not the case and Fig. 

The stability of the concrete mix can be considered in terms of its cohesion , which is a subjective term used to describe its ability to maintain a homogeneous appearance when subjected to applied stress. Lack of cohesion leads to segregation of the mix components into layers relevant to their densities. A further term associated with mix stability is that of bleeding , which is the movement of water to the surface of the fresh concrete. This phenomenon can occur either in isolation or as a manifestation of segregation. Bleeding in excess is normally considered to be undesirable because of the dangers of water runs at the shutter/concrete interface and cracking due to plastic settlements, and there is also the possibility of adverse effect on the concrete-reinforcement bond due to the collection of water beneath the steel. 

Concrete mix number Aggregate type Water-cement ratio Admixture 28-day strength (N mm- ) Modulus of elasticity at 28 days (N mm- )... 

The overall conclusion from the available data is that when a concrete mix is designed incorporating a water-reducing admixture of the normal or retarding type, then the properties of the resultant concrete at 28 days will conform to the normal relationships used for concrete not containing an admixture at the same water-cement ratio. 

Table 1.21 Sulfate resistance of concrete mixes containing water-reducing agents (no mix design changes other than addition of water-reducing admixture)...

It can be concluded from the assessment of the data in this section that inclusion into a concrete mix of a water-reducing admixture of the lignosulfonate, hydroxycarboxylic acid and air-entraining type should not lead to any deterioration in the durability of that concrete to freeze-thaw cycling. Indeed there are strong indications that, when used either as a means of reducing the water-cement ratio or, alternatively, of reducing the cement content, more durable concrete may result. 

When superplasticizers are used to reduce water content of the concrete mix, the increase in strength is normally considered to follow the Abram s... 

The air-entraining admixtures are organic materials, usually in solution form, which when added to the gauging water of a concrete mix, entrain a controlled quantity of air in uniformly dispersed microscopic bubbles. This type of air should not be confused with entrapped air which is often present in concrete in the form of irregularly shaped cavities and which can be due to inadequate compaction or flaky aggregates. 

The mix capacity was also varied using the full-size mixer with the same concrete mixes and admixtures. Results are given in Table 3.10 where it will be seen that the effect of batch size is only slight and, in the higher cement content mixes, shows a trend towards higher air content as the capacity of the mixes is approached. 

Dampproofers based on liquid fatty acids, such as oleic, caprylic and capric, are used as major components in fatty-acid mixtures. A typical example is shown in Table 4.2 [3]. The mixtures are added directly to the concrete mix without predilution, or addition to the gauging water. 

The heat evolution of concrete mixes containing no admixture, 1.5% calcium chloride and 3.0% calcium formate is shown in Fig. 5.18. The heat evolution of calcium chloride and calcium formate are approximately equal at 24 h, which is reflected in similar compressive strengths at this age of 10.0 and 12.5 N mm i. 

Accelerating admixtures reduce both the initial and final setting time of mortar sieved from concrete mixes, determined by ASTM C403 68 or BS 5075 (1975). Typical results are given in Table 5.1 for a 300 kg m cement content mix with a compacting factor of 0.85 0.02 [24] at normal ambient temperature. 

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