New developments in concrete technology

Introduction

The most widely used construction material throughout the world is concrete which is used for building and replacement of new and existing infrastructure. The high attribute to using Portland cement concrete is due to its low cost for maintenance and construction of buildings. There are two driving forces which caused much advancement in concrete technology including concrete durability and the requirement for speedy construction processes.

Emerging developments

There are various pullout tests developed to determine the pouring consistency of concrete to create lightweight concrete and evaluate its holding strength. A combination of low water to cement ratio and consistent mixing has resulted in high compressive strength products (Collepardi, 1994; Fukute, 2005).

The use of less water for each mixing stage can produce the concrete which will take 14 days to balance the moisture content to the atmospheric value. However, there are few technologies that allow the equilibrium to be achieved within 6 days.

The studies showed that the presence of low water content in concrete allows the higher bonding strength with other surfaces including concrete decks and metals. The self-contained concrete mixtures have been developed which are equipped with pumps and foam generating appliances. Some of the new developments which are helpful for the concrete industry are discussed below.

Figure 1: The Concrete USA pumping equipment is fully automated and self-contained. Use to weigh cement and contains foam

Ultra-High Strength Concrete

Unique combinations of superior tensile strengths, durability, compressive strengths and ductility have been achieved in high-strength concrete through recent developments. The more durable and lighter structures can be constructed by the use of ultra-high strength concrete for given conditions of structure loading. Structures constructed with ultra-high strength concrete require less energy and raw material with fewer generations of CO₂ emissions (Malhotra, 1997).

The reduced value of low w/cm has resulted in the production of low permeable material which has high durability even in aggressive and rough environments. High-strength concrete has also been preferred in applications which require high durability rather than high strength. Such applications include the construction of undersea tunnels, offshore platforms of oil, bridges with long spans and all other marine concrete structures. The development of super plasticized concrete with high strengths has also been observed with the need to increase material fluidity in the absence of segregation (Sivasundaram, et.al, 1994). 

There are various admixtures which can be used to improve the workability of the super plasticized concrete. The most common admixtures with cementitious and pozzolanic characteristics include fly ash, furnace slag with ground granulated base and silica fumes (Morgan, 1994).

Figure 2: Porosity vs. strength relationship source: (Beaudoin and Ramachandran, 1992)

The construction costs have been reduced significantly because of the facilities provided by the new developments in concrete technology e.g. ease in the formation of concrete mixing and pumping processes. The construction of offshore structures and high-rise buildings are examples of structures with resulted in lower costs. The fabrication of the pre-stressed concrete and heavy reinforcement with narrow spaces is a special case of the new technology.

High-performance concrete

The concrete mixtures with special characteristics of high strength, high workability and high durability are termed high-performance concrete. The mandatory requirement of high durability made high-performance concrete distinct from high-strength concrete. Sometimes the concrete mixtures are developed to be applied for applications where high dimensional stability is required.

The achievement of a highly durable mixture of concrete under numerous environmental conditions requires a crack-free structure during all of its service life. The limiting of paste content of the cement mixture within a concrete mixture is required to avoid cracks in a structure as a result of drying and thermal shrinkage. The new technologies have proposed the proportioning procedures of high-performance mixtures (Malhotra, 1994).

The proportioning method proposed the limiting content of cement pastes up to one-third by the total volume of the concrete. The Portland cement has been permitted to be partially substituted by the use of admixture i.e. pozzolanic or cementitious. The use of ternary blends of cement that contain silica fumes, slag, fly ash, limestone, rice husk and methacholine has been preferred by many new technologies (Roy and Silsbee, 1994).

The use of these elements has resulted in synergetic effects by the improvement of the concrete properties in the form of its freshness and hardness which also has made the high-performance concrete more economical.

Carbon Dioxide Absorption

The new technologies have found that concrete can absorb CO2 from the atmosphere. The studies have concluded that the mechanism of carbonation in concrete is responsible for more than 50 percent of the emission of CO2 during the production of original cement. Various technologies have been developed for the effective mitigation of CO2 emissions and thus to protect the environment from hazardous compounds (Hayakawa, 1995).

Figure 3: Depth of carbonation source: (Beaudoin and Ramachandran, 1992)

Nanotechnology

Nanotechnology is one of the most active areas of research throughout the world. The world of nanotechnology has been successfully applied in various research topics including machine components, electronics and biomechanics. There are many new investigations made by researchers in the field of concrete composition through the application of nanotechnology. The emerging researchers in developing the new developments in concrete technology include (Richard and Cheyrezy, 2004).

The clinkering temperature during the production of cement can be reduced greatly by the introduction of nanocatalysts (Mehta and Aïtcin, 1990). The development has also resulted in the reduction of CO2 emissions and consumption of energy during cement production.

Figure 4: Hydrated cement paste of 0.55 W/C concrete, where A = CH, B = C-S-H, and

C = ettringite needles

Other developments include the use of nano-silica (nanoparticles of silicon dioxide) in ultra-high performance concretes. The cementations components have been developed which are based on nano-engineered particles and nano binders. The stronger, durable and ductile cement can be obtained by the incorporation of a concrete mixture with carbon-based nanotubes with more sustainability. For water reduction and complete workability control, a new development has been made in the generation of superplasticizers.

Cathodic protection of reinforced concrete

The flow of current in the galvanic cells can be suppressed by the use of techniques involving cathodic protection. The techniques use superficial anodes and supply current from opposite directions. The reinforced structures of concrete contaminated with chloride can be protected against corrosion by the use of the method of externally applied current.

Figure 5: Depth of chloride penetration source: (Beaudoin and Ramachandran, 1992)

The researchers showed that the buildup of the ions of potassium and sodium results in the bond degradation between concrete components i.e. steel. The softening of the interface of steel and concrete has been observed due to the buildup of such ionic bonds (Swamy and Tanikawa, 1990). The increase of chloride content of the concrete increases the current density and thus the bond degradation of steel and concrete interface.

The researchers showed that the buildup of the ions of potassium and sodium results in the bond degradation between concrete components i.e. steel. The softening of the interface of steel and concrete has been observed due to the buildup of such ionic bonds (Swamy and Tanikawa, 1990). The increase of chloride content of the concrete increases the current density and thus the bond degradation of steel and concrete interface.

Surface coatings

The concrete surfaces can be protected effectively from external attacks by the barrier or surface coating.  There is a wide range of barrier coatings available to protect the concrete surface from deteriorating effects. The new developments have found the role of diffusion characteristics of the various coatings which have similar generic properties to the contents of concrete.

Figure 6: Visual corrosive attack on steel embedded in concrete