Portland cement-based concretes

An exposme to elevated temperature (up to 600°C) tends to increase the strength of microsilica-modified Portland cement based concrete. This may be attributed to the formation of additional C-S-H in a reaction between residttal calcium hydroxide and microsilica (Saad et al, 1996). 

The development of calcium aluminate cement was spurred by efforts to overcome the problems associated with sulfate attack on Portland cement based concrete used in the construction of railway tunnels in gypsiferous grounds. The first patent relating to this type of binder was filed in 1908 by Bied in France. The cement was introdueed into production in 1913, and became known as Ciment Fondu. After it was recognized that calcium aluminate cement gains strength much faster than Portland cement, the binder was used in World War I by the French military in the constraction of gun emplacements and shelters, where this property was of paramount importance. After the war, the cement became widely used in other structural applications however, its use in this area became limited, after failures of structures built with this cement were reported from different countries. Nowadays calcium aluminate cement is being used in a variety of special applications. 

The hardened magnesium phosphate paste and concrete mixes made with this binder exhibit an excellent bond to old Portland cement based concrete, and are very suitable for repair works on existing concrete structures, such as patching of potholes on highway... 

The term high-performance concrete (abbreviation HPC) is not defined precisely. Such concretes are understood to have compressive strengths exceeding distinctly those of normal, ordinary Portland cement based concrete, typically in the range 75-100 MPa or above. 

Figure 18.2 Effect of microsilica (MS) addition on compressive strength of Portland cement based concrete at equal slump values [W/(C+MS) =0.30].

Normal Portland cement based concrete exhibits a low reflectibility and a high transmissivity to radio waves. This ratio may be reversed by incorporating small amounts (0.5 vol.%) of caibon filaments in the mix. In such mixes the absorbed radiation is negligible, compared with the reflected radiation (Fu and Chung, 1998). Concretes of this type may be potentially useful for lateral guidance in automatic highways. 

Chloroaluminates Chemical compounds formed in concrete when chlorides combine with the C A in the hardened cement paste. These chlorides are no longer available to cause corrosion. Sulphate resisting cements have a low C A content and are more prone to chloride induced corrosion than normal Portland cement based concretes. 

Portland cement-based concretes are the most widely used in the construction industry. Non-portland cement-based systems, particularly those that have fast hardening and strength development characteristics, are well suited for special applications, many of these related to the repair of concrete structures. 

The water requirement of alkali-activated slag cements is relatively low, owing to the plasticizing effect of the alkali compounds that are present, resulting in a lower total porosity of the hardened material, as compared with Portland cement mixes. The produced fresh AAS cement based concrete mixes exhibit a distinct thixotropy and require continuous mixing, to prevent a quick slump loss and setting. Owing to their thixotropic properties even stiff mixes may be compacted if vibration is applied. 

Harmant, D.J. (1998) Durabihty of polypropylene fibers in Portland cement-based composites eighteen years of data. Cement and Concrete Research 28,1809-1817. 

Hills, C.D., Sollars, C.J., and Perry, R. (1993) Ordinary Portland cement based solidification of toxic wastes the rote of OPC reviewed. Cement and Concrete Research 23,196-212. 

Hansson, I.L.H. (1983) Electrical resistivity measurements of Portland cement based materials. Cement and Concrete Research 13,675-683. 

Cement mortars and concretes have been used extensively in their present form since the beginning of the nineteenth century. There is no need to set out here their history or to describe their properties and applied technologies, because nearly every year several excellent books are published on these subjects. However, there is perhaps at present a new phase of development of Portland cement-based materials, stimulated by the following factors ... 

The composites with brittle and ductile matrices are distinguished with respect to the matrix behaviour. The Portland cement-based materials belong to the group of brittle matrix composites as well as materials with ceramic matrices. Also, resin concretes which behave basically in a ductile manner may show some brittleness in particular conditions in low temperature or when subjected to high rate loadings. 

The performance of many non-portland cement-based repair materials is dependent on the chemistry and physics of the system, the properties of the existing concrete, and the enviromnent. Thermal analysis techniques are increasingly being used to investigate the physico-chemical behavior of non-portland cement binders exposed to aggressive enviromnents. 

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystalforming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) can be selected for specific chemical exposures. 

Concrete is a particulate composite of stone and sand, held together by an adhesive. The adhesive is usually a cement paste (used also as an adhesive to join bricks or stones), but asphalt or even polymers can be used to give special concretes. In this chapter we examine three cement pastes the primitive pozzolana the widespread Portland cement and the newer, and somewhat discredited, high-alumina cement. And we consider the properties of the principal cement-based composite, concrete. The chemistry will be unfamiliar, but it is not difficult. The properties are exactly those expected of a ceramic containing a high density of flaws. 

The concrete material used for sewer construction is typically based on the use of Portland cement. Different types of Portland cement have not shown significant differences in the corrosion rate of concrete. However, an increase of the relative amount of cement used in the concrete reduces the corrosion rate— in units of mm y-1—according to the increase in the alkalinity per unit volume of the concrete material (Grennan et al 1980). The use of high-alkaline materials... 

Fig. 2.19 Strength development of high-strength flowing concrete containing melamine-based superplasticizer compared to concrete made with 400 kg of normal Portland cement per m in the stiff to low workability ranges (25-100 mm slump). 

Two types of calcium nitrite-based corrosion inhibitors are currently marketed, viz. a set- and strength-accelerating type and a normal-setting type. The former increases the early strength development in concrete. This effect increases with the dosage. Both admixtures are compatible with all types of Portland cements and... 

An alternative to silicate-based Portland cement is the calcium aluminate cement, ciment fondu, which originated with the Lafarge company in France in 1908. Ciment fondu is typically made by heating limestone with bauxite, which is mainly AIO(OH) but contains much iron oxide (see Section 17.2). As noted above, calcium aluminate hydrates and hardens much more rapidly than alite, and so ciment fondu, either as such or mixed with Portland cement, can be used whenever a rapidly setting cement is required, for example, for construction at low temperatures. Concretes made from aluminate cements remain serviceable at higher temperatures than Portland cements and so are used to make cast refractories for pyrometal-lurgical applications. 

Based on this experience and applied to a spread of ready-mix concrete cost of 40 to 80 a yard and extended to a range of quantity of sulfur concrete mixed per day, there is an indicated cubic yard comparison, materials only, of approximately 1% to 6 times the cost of Portland cement concrete for sulfur concrete. Greater volumes per day yield lower unit costs. Experience at Corpus Christi would put the premium cost of sulfur concrete approximately 15 pet more than the cost of Portland cement concrete. 

---