It is also regarded as preparation for shotcrete and/or rock bolts. Shrinkage-compensating concrete is the subject of ACI 223-98 [73], where expansion is restrained by steel reinforcement (preferably triaxial) so that compression is induced in the concrete, which offsets the tension in the steel reinforcement induced by restraint of drying shrinkage. Type II has moderate sulfate resistance, with or without moderate heat of hydration (modified). If the joints fill with incompressible material during the winter, concrete expansion during the summer can cause pavement blowups. After excavation, temporary support must be provided to prevent rock fall or collapse. The speaker held his ground, however, and said that concrete doesn't expand. This term is commonly, but loosely, used to describe any formed gapped joint, whatever its structural role and irrespective of whether opening or closing movements are expected. 4.24) to exhaust smoke, poisonous gas, and dust that are produced while drilling and blasting. Figure 4.23. Emulsions. The gypsum level is increased slightly. Table 9.19. L1=Measurement is taken after 24 hours of immersion in water at a temp. C. David Lawrence, in Lea's Chemistry of Cement and Concrete (Fourth Edition), 1998. They have the advantage of enabling fast and easy connection of all detonators at one ignition point (compared to the time-consuming and complicated process of connecting electric detonators). Type I cement is generally supplied unless another type is specified. Increasing the Fe2O3 content in the feed resulted in a lowering of the clinkering temperature. The SO3 content of the clinker is up to 10 per cent.78 The designation C4AF does not imply a particular member of the ferrite solid-solution series. re expansion of cement The Le Chatelier procedure determines unsoundness from the hydration of free CaO only, whereas the autoclave procedure measures cement paste expansion from either free CaO, free MgO, or both. 4.25). They are used in conjunction with shotcrete and act as armor to achieve a good level of support in tunneling. It is available only on special order for very large tonnages with long lead times, if at all. This is followed by application of an appropriate primary support. While, in theory, you can cut an expansion joint in concrete at any time, it’s better if this i… Expansion joints allow independent movement between adjoining structural members, minimizing cracking when such movements are restrained. However, such systems can be expected to have a different pH response to acid addition than cements based primarily on CSH. However, concrete does indeed expand when it gets hot or when the moisture content changes. 4.31) is normally used for classes IV and V whose span is less than 18 m. There is a greater chance of settlement and the middle temporary support has to be removed later. The coefficient of thermal expansion or CLTE, Coefficient of Linear Thermal Expansion. Percentages of C2S and C4AF are relatively high, while C3A and C3S are low compared to other types. If it is the reinforced concrete, the concrete will bear compressive stress in order to achieve pre-stress. Rock behavior and water infiltration are also noted. The expansive cement can be divided into expansive cement and self-stressing cement according to different expansion ratios. New York, NY: McGraw-Hill. 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Conventional tunneling has the following steps (Fig. Anchors and rock bolts are active reinforcing elements designed to anchor and stabilize the rock mass during tunnel excavations. The latter involves the installation of steel sheets or bars. 4.39). A concrete expansion joint – or control joint – is a gap which allows the concrete to expand and contract as/when the temperature changes. Nevertheless, muck in the upper stage may influence the construction of the lower stage. Pumpable, resistant to water, and thus growing in use. George C. Wang, in The Utilization of Slag in Civil Infrastructure Construction, 2016. The coefficient of linear thermal expansion (CLTE) of any material is the change of a material's dimension per unit change in temperature. This cut is suitable for rocks with fractures. It is also possible to use expansive cement to make self-stressing concrete, in which there is a residual compressive stress (say, up to 7 MPa) after most of the drying shrinkage has occurred; hence, shrinkage cracking is prevented [1,6]. Waterproof cement is mainly used in impermeable hydraulic construction, water supply and drainage structures (such as pool ands water towers) and underground structures, and waterproof roofs. Before blasting it is necessary to drill holes in the rock to insert explosives. In case of rock mass movement, the bolts will develop a restraining force that is transferred back to the rock mass as in Fig. Calculate the mean values of two measurements, to the nearest 0.5 mm. Most of these physical tests are carried out using mortar or paste created from the cement. The material is conveyed in a dry or semidry state to the nozzle, where water is added to the mix before being applied at high velocity onto the substrate. Iron-rich cements in the system C2S-C4A3S¯ have been examined; Table 9.19 summarises the results of an early investigation.26 Cements fired at the lower clinkering temperatures possible (1200°C for 1 h), show that C4AF is formed with increased hydraulic activity and practically no free CaO. The hydraulic character of these ferrites is greatly influenced by the speed of quenching.128 The possibility of forming C4F3S¯ was not confirmed.128 Compressive strengths were measured on 10 mm cubes, at water/cement = 0.3 and the degree of hydration is established by quantitative X-ray diffraction. The hydration of samples of C3A and C2(A,F) (obtained by extraction from Portland cements) show that the ferrite hydrates more rapidly in the presence of calcium sulfate. The expansion mechanism is the expansion of ettringite generated in cement paste. a relative of portland cement that contains materials that increase in volume as they set. To make enough room to operate and ensure a good environment for workers in the tunnel, muck should be removed. Detonating cords. The expansion includes existing approval for the company’s cement plant at Pali, Rajasthan, and its 6.7-MTPA capacity addition currently underway in Uttar Pradesh, Odisha, Bihar and West Bengal, which is expected to be commissioned by FY22 in a phased manner, UltraTech said. Thermal expansion and contraction of concrete varies primarily with aggregate type (shale, limestone, siliceous gravel, granite), cementitious material content, water cement ratio, temperature range, concrete age, and ambient relative humidity. The hydration products formed from calcium aluminoferrite cements in the presence of gypsum have been studied:129 the hydration products were essentially similar to those formed from C3A. Certain cement has been found to undergo a large expansion after setting causing disruption of the set and hardened mass. Thermal expansion coefficients for some common materials: 10-6 m/moC = 1 μm/moC m/m = meter per meter, in/in = inches per inches Most values for temperature 25 oC (77 oF). Expansive cement can generate volume expansion in the hydration process, and it does not shrink but also expand to some extent. Concrete construction handbook (4th ed.). Bound by the conditions, it can improve the pore structure of concrete and reduce pores and porosity to improve the density and impermeability of concrete. Electric detonators (Fig. Table 13.1. The coefficient decreased with increase in the water-cement ratio, increased with age, and was smaller below the freezing point of the concrete. By adjusting the coordinate proportion of the above four types can generate the expansive cement with different expansion ratios. The linear expansion of a heated solid (or liquid) is measured by Expansion Joints In Concrete. Firing temperatures were low, in the region of 1250°C, leading to good grindability; their properties could be adapted by varying the proportions of clinker minerals to give either high early strengths or, The National Standards Compilation Group of People’s Republic of China, 1994, U.S. Department of Transportation Federal Highway Administration (FHWA), 2009, Journal of Natural Gas Science and Engineering. In chemical prestressing the tendons are placed untensioned in the forms and the concrete is poured. Explosives are then pumped down the hole around the detonator and primer, before the end of the holes are filled with stemming. 4.34) uses this construction method. Figure 4.33. The composition of alunite is [K2SO4 • Al2(SO4)3 • 4Al(OH)3], and it can generate ettringite, the best expansive cement at present. This cement has so far found a more limited application than the other two types because of the difficulty of steadily controlling the rate of formation of ettringite from tricalcium aluminate. The company is currently expanding its capacity at Siliguri, West Bengal. When the Al2O3/Fe2O3 ratio is low (<1.0), belite and a high ferruginous ferrite, C6AF2 is formed containing significant amounts of SO, in solid solution. Commercial clinkers containing sulfoferrites can form at temperatures between 1200 and 1350°C, to produce cements showing high resistance to sea water, and 28-day strengths of >80 MPa.130, The aluminoferrite phase has a variable composition, even within individual clinker nodules,131 and this phase can accommodate ∼10 per cent by oxide mass of impurity ions.46 Heterovalent substitution in the lattice leads to greatly increased hydraulic activity and to a near-amorphous structure. Modified is used when optional additional requirements are invoked such as moderate heat of hydration and low alkali. Even after 7 days, the unreacted tricalcium aluminate content is still appreciable. Of these factors, aggregate The former is the insertion of tensile strengthening elements in the ground such as dowels. There are “smart” materials that allow us to envision self-stressing with effective prestress levels that can be controlled much more accurately, and can be of much larger magnitude than is achieved with expansive cement matrices or electrical prestressing. Expansive cements are used generally to minimize cracking caused by drying shrinkage in concrete slabs and pavements structures and in special circumstances, such as prevention of water leakages. 4.32) is used for fractured rocks as it provides top and lateral supports. Shape memory alloys (SMAs) and some special polymeric fibers possess the unique property of being able to be frozen temporarily in a particular state, then, with proper heat or radiation treatment, go back to their previous equilibrium state. When the stage is 3–5 m long (K=3–5 m), it is known as an ultrashort stage method. Hydration studies in the system C2F-C4AF-C4A3S¯ showed that C4AF hydrated more rapidly than C2F and that the presence of C4A3S¯ accelerates the hydration of the ferrite. The cements gave a high resistance to sulfates (tested over 12 months). The linear expansion rate of expansive cement is generally under 1%, equivalent to or slightly larger than the shrinkage rate of ordinary cement, which can conduct shrinkage compensation. That's why you need expansion joints in bridges, buildings, and other structures. This method is typically useful when the area of excavation is in fragmentary strata. Fe(OH)3 was found as a gel phase and Fe3+ ions were incorporated into the AFm hydration products. A tunnel jumbo drilling rig. This type of cement is specified in concrete exposed to seawater. The self-stressing cement can be used for pressure tubes and fittings in self-stressing reinforced concrete. The value of its expansion can be adjusted by changing the content of aluminate cement and gypsum. At early ages the kleinite phase hydrates more rapidly than the tricalcium aluminate. To avoid problems associated with drying shrinkage of concrete, it would be advantageous to use cement that does not change its volume due to drying shrinkage or, sometimes, that even expands on hardening. The cements were formed by melting at 1360°C and then hydrated after cooling and grinding with 3 per cent gypsum (Table 9.18) to 300 m2/kg. The reaction rate normally remains relatively high until depletion has taken place. 4.29): A small section of long-stage excavation (K>50 m) is needed to maintain the stability of the excavation face. The reaction rate of the ferrite phase in Portland cement is increased by the presence of 1–3 per cent potassium citrate or potassium carbonate, or combinations of the two. Scaling: (A) manual scaling and (B) mechanized scaler (Mining & Construction, 2013). Three main types of expansive cement can be produced—K, M, and S—but only type K is commercially available in the United States. 4.26). Heat of hydration is less than for other types, and the heat develops more slowly. The three types are: Parallel cuts. The mineral composition is C4A3S¯ (35–60 per cent), C4AF (15–45 per cent) and C2S (15–30 per cent). The hydrates forming are AFt, AFm, AH3 and C-S-H; strengths in the range 50–90 MPa at 1 day are achieved, with good frost resistance. The aluminoferrite phase in Portland cement clinker contains considerable quantities of MgO, Mn2O3 and TiO2.46. Although the pH stability of ettringite has not been specifically addressed, some studies, both in the areas of cement and concrete, and waste management, have touched on this issue. Type IV is low heat cement. While hauling, niches or bays are needed for trucks to turn around when the tunnel is small (Fig. Chemical prestressing, however, does not belong to any of the above. CD excavation (midwall method, Fig. But the industry is seeing an alarming number of panel failures resulting in costly building repairs. Four-component clinkers containing Al2O3, Fe2O3, CaO and SiO2 with additions of SO3 and MgO may be synthesised, at varying Al2O3/Fe2O3 ratios, at 1350°C followed by either slow cooling or air quenching. One hundred and twenty-five 3 x 4 x I2 in, (7.6 x IO x 30.5 cm) reinforced concrete prisms were tasted for thermal coefficient of expansion. I beam girders (Fig. 3Al2O3 CaSO4) and either gypsum or an anhydrite gypsum mixture. The linear expansion rate of expansive cement is generally under 1%, equivalent to or slightly larger than the shrinkage rate of ordinary cement, which can conduct shrinkage compensation. A.: When it first dries, concrete shrinks and undergoes structural alterations that make some of the shrinkage irreversible. A short-stage method (K>5–50 m) can improve the stress conditions of initial supports to control the deformation of surrounding rocks. Nonelectric detonators. Types I, II, and III are normally readily available in all local market areas. L2=Measurement was taken after 3 hours of immersion in water at boiling temperature. The hydration of calcium sulfoferrites and the addition of sulfoferrite clinker to Portland cement results in improved properties for the cement.130 In the C-F-CS¯ system, clinkering starts at 800°C with the formation of CF initially. 1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Ventilation is necessary to secure a safe and healthy working environment in the tunnel (Fig. Other properties, such as rapid hardening and high early (1–3 days) and late (28 days) compressive strength may be the desired purpose. As an example, the application conditions of the excavation methods are introduced here, according to the Chinese code rock classes (Table 4.1). In exterior concrete, joints widen during cold weather because of cooling contraction and get narrower during hot weather as the concrete expands. The expanding agent is obtained by burning a mixture of gypsum, bauxite, and chalk, which form calcium sulfate and calcium aluminate (mainly C3A). When this ratio is high (1.75), the sulfate is first consumed to form C4A3S¯ and a high Fe2O3 aluminoferrite phase (C6AF2), in spite of the high aluminate composition of the clinker, as well as β- and α′-belites. The drilling angle is hard to control. 4.37) are lightweight triangular steel frames. General procedure of drill-and-blast method. Expansive cements consist of a mixture of Portland cement, expanding agent, and stabilizer. They were burned in an electric oven at 1350°C for up to 35 min. They are applicable to all kinds of rock and no large-diameter drilling machine is needed. Bai Yun, in Underground Engineering, 2019. That's why you need expansion joints in bridges, buildings, and other structures. 4.23) used to initiate explosives such as blasting works in noncoal mines, open pits, and demolition and other engineering projects. Figure 4.25. Figure 4.35. This will cause serious difficulties for the durability of structures when such cement is … Ghorab and Kishar (1986) found the pH of an ettringite solution to be 11.2, whereas a group of workers based at the University of North Dakota have variously observed pH values from 9.8 to 12, although their most recent work states that ettringite is not stable below pH 11 (McCarthy, Hassett and Bender, 1992, Kumarathasan et al., 1990, and Hassett et al., 1989). Thus it is also called shrinkage-compensating cement or the non-shrinkage cement. Factors such as cementitious material content, water-cement ratio, temperature range, concrete age, and ambient relative humidity can also influence the thermal properties of concrete. A normal Portland cement and a sulfate-resisting Portland cement clinker were examined.126 Compressive strengths of cement mortars were measured on 40 × 40 × 160 mm prisms between 4 h and 28 days; after 28 days, strengths lay between 56 and 81.5 MPa. This type is used in concrete exposed to alkali soil-borne sulfates and groundwater sulfates (Dobrowolski, 1998). Firing temperatures were low, in the region of 1250°C, leading to good grindability; their properties could be adapted by varying the proportions of clinker minerals to give either high early strengths or expansive cements. High early strengths were obtained from high-iron mixes containing C4AF.122 The hydration of C4AF synthesised by solid-state reaction at 1200°C, was faster than that for C4AF synthesised from the melt.124 Compressive strengths have been reported for ferrites prepared by the separate burning of pure compounds;123 the ferrites were fired at temperatures such that the free lime was reduced to zero (1230–1350°C). A mixture of limestone, gypsum, bauxite, silica sand and iron-rich industrial by-product raw meal (in carefully selected proportions) which was sintered at 1280°C and ground to 3700 cm2/g, with no gypsum being ground in, gave such a cement.321. Type III is high early strength cement. The addition of alunite expansive agent and aluminate expansive agent into Portland cement will also lead to the expansion of cement. This cement is used for massive concrete structures with low surface/volume ratios. Due to its danger, the safety of workers must be carefully considered. 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