Water-binder ratios

Table 11.8 Critical chloride content for different environments and water-binder ratios for concrete made of ordinary Portland cement (% by mass of binder), from DuraCrete [21]...

High performance concrete (HPC) may be defined as a concrete that, with particular care in the selection and proportioning of its constituents, shows a clear improvement in one or more of the properties with respect to ordinary concretes [1]. In practice, the term high-performance concrete is applied to concretes with a low water/binder ratio (0.3-0.35 or even lower), elevated cement content (400-550 kg/m ) and the addition of 5-15% silica fume with respect to the total mass of binder. Sometimes fly ash or GGBS are also added. In order to achieve a suitable workability with mixes typical of HPC, a high dosage of superplasticizer is required. 

Hydrophobic Agents used as Concrete Admixture. In order to investigate the resistance of the concrete against chloride penetration, five concrete mixtures with increased additions of a silane-based hydrophobic admixture (Protectosil) [4], were produced (Table 1). The binder was based on a blended cement of type CEM II/A-V 42.5 with approximately 20 % fly ash in combination with silica fume (5.3 %). A total binder content of 412 kg/m gave a water/binder ratio of 0.40. The hydrophobic admixture was added to the fresh concrete mixture in the form of a powder in quantities of 0.5, 1.0, 2.0 and 4.0 % by weight of cement, respectively (P0.5 - P4.0). A reference mixture without any hydrophobic admixture (PO.O) was also produced. 

A part of cement in concrete production can be replaced by siliceous fly ash. The quantity of fly ash addition is then determined according to PN-EN 206-1 Standard, which is introducing k coefficient and the maximum fly ash/cement ratio cannot be higher than 0.33. The water/binder ratio can be calculated using this... 

The strength of the hardened paste depends mainly on its overall porosity, which is determined by the initial water/binder ratio. To a lesser extent the strength may also be affected by the size and shape of the formed dihydrate crystals, which may be altered by the hydration temperature and by chemical additives (Rossler and Odler, 1989). 

Figure 2.5 Influence of mixing on rate of hydration. Twelve grams of cement, 20 g of quartz powder and 16 g of water (water-binder ratio = 0.40 w/c = 1.33) were either mixed by hand or mixed using a high-speed mixer at 1600 revolutions per minute (rpm). (Courtesy of Elise Berodier, cole Polytechnique Federale de Lausanne, Switzerland.)...

Figure 2.23 Influence of the amount of anhydrite added on the hydration kinetics of ternary binders based on portland cement (PC), calcium sulfoaluminate cement (CSA) and anhydrite hydrated at 20°C and at a water-binder ratio of O.SO. Citric acid (0.27 mass% referred to binder) was added as set retarder. (Adapted from Pelletier, L. et al.. Cement and Concrete Composites, 32(7), 497-507, 2010.)...

The water-cement ratio (W/C) and unit cement content (C) of latex-modified concrete can be generally expressed as a function of the binder-void ratio (a) with every polymer type at each polymer-cement ratio by the following equations ... 

Latex-modified mortar and concrete are made by using a composite binder of inorganic cements and organic polymer latexes, and have a network structure which consists of cement gels and microfilms of polymers. Consequently, the properties of the latex-modified mortar and concrete are markedly improved over conventional cement mortar and concrete. The properties of the fresh and hardened mortar and concrete are affected by a multiplicity of factors such as polymer type, polymer-cement ratio, water-cement ratio, air content, and curing conditions. 

Effects of Control Factors for Mix Proportions. The binder of latex-modified mortar and concrete consists of polymer latex and inorganic cement, and their strength is developed as a result of an interaction between them. The polymer-cement ratio has a more pronounced effect on the strength properties than the water-cement ratio. However, this effect depends on polymer t3rpe, air content, curing conditions, etc. The relation between the strength properties and polymer-cement ratio has been discussed in a number of papers.P l 1 1 A general trend which summarizes the results obtained in these papers is presented in Fig. 4.19. 

For the purpose of developing the equations for the compressive strength prediction for latex-modified mortars and concretes, all-inclusive consideration of various factors such as polymer-cement ratio, water-cement ratio, and air content is required. Expanding Talbot s void theoryP on ordinary cement mortar and concrete, OhamaP P l defined binder-void ratio (a) or void-binder ratio (P), and empirically proposed the equations using a and p to predict the compressive strength of the latex-modified mortars and concretes as follows ... 

Ultimately the resistance to snlfates will depend not only on the type of cement used, but also on the cation with which is combined, on the concentration of the sulfate in solution, on the condition of exposure to the sulfate solution, and on the amount of the binder in the concrete mix and the water/cement ratio employed. In general, the sulfate resistance will increase with increasing amount of cement employed and with decreasing water/cement ratio. 

Concrete based on calcium aluminate cement performs rather well if exposed to sulfate solutions, especially if made with a low water/ cement ratio and high cement content. However, cases of expansion and cracking have also occasionally been reported (Scrivener and Capmas, 1998). The reasons for the good sulfate resistance of this type of cement are not obvious. It is mostly attributed to a surface densification of the hardened material, resulting in a very low permeability of the formed surface layer, and/or to the absence of calcium hydroxide in the system (Scrivener and Capmas, 1998). Unlike Portland cement and related binders, magnesium sulfate solutions are less aggressive to calcium aluminate cement than alkali sulfate solutions. This is due mainly to the absence of the C-S-H phase in the hardened calcium aluminate cement pastes, which is particularly sensitive to the action of magnesium sulfate. 

Figure 15.1 Effect of fiber type on composite flexural behavior. Mixing ratios—Silica fumeiordinary Portland cement=0.195, water binder=0.21, sand binder=0. Source Reprinted from Linton JR, Bumeburg PL, Gartner EM, Bentur A, Mat Res Soc Symp Proc, 211, 255-264, 1991.

In the test, the mix proportions of different mixes (the ratio of water binder sand aggregate ) were almost the same with different dosages of fly ash, slag and natural pozzolan. From Fig.5, we can deduce some interesting observations ... 

The effects of water content and compaction on two selected mixtures of materials were then investigated. Mixes were made using various water-to-binder ratios, and compacted using a metal tamper to achieve the maximum possible compaction. Results of compressive Strength testing are presented in Table 27. 

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