Binders (Cement)

Cement to the standard

Cement : is the hydraulic binder (hydraulic = hardening when combined with water) which is used to produce concrete. Cement paste (cement mixed with water) sets and hardens by hydration, both in air and underwater.

The main base materials, e.g. for Portland cement, are limestone, marl and clay, which are mixed in defined proportions. This raw mix is burned at about 1450°C to form clinker
which is later ground to the well-known fineness of cement.Cement to the standardThe standard divides the common cements into 5 main types, as follows: ·     CEM I:               Portland cement
·     CEM II:             Composite cements (mainly consisting of Portland cement)
·     CEM III:            Blast furnace cement
·     CEM IV:            Pozzolan cement
·     CEM V:              Composite cement
 Under the above table, the various types of cement may contain other components as well as Portland cement clinker (K):Major components

Granulated slag                                              (S)

Silica dust                                                         (D)

Natural and industrial pozzolans            (P or Q)

High silica and limestone fly ashes        (V or W)

Burnt shales (e.g. oil shale)                      (S)

Limestone                                                       (L or LL)

Terms of Concrete Constituents

Terms of Concrete Constituents

Three main constituents are actually enough to produce concrete:
·     Binder (Cement)
·     Aggregate
·     Water
 Due to continually increasing demands for the concrete quality (mainly durability) and huge advances in admixture and concrete technology, it is now possible to produce many different kinds of concrete.·     Standard concrete:               Concrete with a maximum particle diameter > 8mm Density (kiln dried) > 2000 kg/m³,maximum 2600kg/m³
·     Heavyweight concrete:        Density (kiln dried) > 2600 kg/m³
·     Lightweight concrete:          Density (kiln dried) > 800 kg/m³ and < 2000 kg/m³
·     Fresh concrete:                      Concrete, mixed, while it can still be worked and compacted
·     Hardened concrete:              Concrete when set, with measurable strength
·     Green concrete:                     Newly placed and compacted, stable, before the start of detectable setting (green concrete is a pre-casting industry term)
 Other terms in use are concrete, pumped concrete, craned concrete etc.

Cementitious materials

Cementitious materials

Concrete performance is largely dependent upon the properties of the cementitious materials, particularly the chemical properties. Understanding the complex manner in which cementitious materials interact requires career dedication. Producers of high-strength concrete do not have to become experts, but they should at least appreciate that the cementitious materials chosen are supremely important and be knowledgeable with respect to the characteristics to look for. Given the complexity, cement hydration is best thought of as a process that takes place in a “black box.” A producer’s time would be best spent evaluating what should go into the box in anticipation of what should come out. Trying to understand the mechanics of what actually happens inside the box can lead to confusion or misunderstanding, and is best left in the hands of the cement chemists.

Principles of concrete proportioning

Principles of concrete proportioning

The term “principles of concrete proportioning” is used frequently. A primary facet of high-strength concrete technology is that the empirical relationships best suited for determining the quantities of each constituent material is quite different than for conventional-strength concrete. The objectives of the proportioning process remain unchanged; however, the paths, or “principles” required to satisfy those objectives are often very different with high-strength concrete. For example, the size and quantity of coarse aggregate necessary to achieve optimum strength performance at a given age depends on the target strength under consideration. Common objectives include satisfying requirements for strength, durability consistency (slump or slump spread), pump ability, workability, or setting time. Less common, but equally important objectives, if necessary, might involve satisfying requirements for modulus of elasticity, creep, heat of hydration,or shrinkage.

The relevancy of the slump test

The relevancy of the slump test

The slump test is one of the oldest and most frequently used tests to measure the consistency of fresh concrete. Consistency refers to the relative mobility or ability of freshly mixed concrete to flow. Common terminology used to describe the consistency of fresh concrete include stiff, plastic, normal, flowable, and fluid. Workability refers to the relative ease at which freshly mixed concrete can be placed, consolidated, and finished. Though frequently used inter changeably, the terms consistency and workability are independent concrete properties. This misconception is most likely based on the false presumption that as the concrete slump increases, so does workability. Whether or not increasing slump improves or worsens workability depends on several factors, including aggregate grading, cementitious materials content, and W/B ratio.

 By definition, slump is a measure of the relative stiffness, or consistency of fresh concrete. It is not a measure of workability, water content, or W/B ratio. Procedures for performing the slump test are described in ASTM C143.4 A very popular misconception within the industry is that a strong correlation exists between slump and water content. Slump is influenced by many factors in addition to water content. Even in concrete, where consistency is not produced with the aid of water-reducing admixtures, there is no reliable correlation between slump and water content. Other factors influencing slump, include, aggregate cleanliness and aggregate particle grading. For example, measures taken to improve aggregate grading will usually result in a reduction in water demand. If the same quantity of water were used to produce the concrete, the consequence of using aggregates having better grading uniformity would be an increase in measured slump. If, on the other hand, the water content was not adjusted, the increased slump might exceed the maximum prescribed limit when tested at the job site, and forming a basis for rejection, even though the W/B ratio remained unchanged.

 For the slump test to be relevant, the concrete must be of a plastic and cohesive consistency. Lean concretes often lack enough cohesion to prevent the slump test sample from shearing off to one side. The slump test is not suitable for measuring the consistency of very stiff or flowing and self-consolidating concretes. High-strength concrete is a cohesive material, and most modern high-strength concrete is placed at flowing or fluidized consistencies. High-strength concrete produced using well-graded aggregates usually do not exhibit segregation at measured slumps below 250 mm(10 in) or below. Measuring the diameter of spread of the slump sample rather than the vertical drop distance is a more relevant method for determining the consistency of flowing and self-consolidating concretes.

 The slump test has little relevancy with super plasticized flowing concretes, and it is not recommended that the slump test be used as an acceptance test. If the slump test is used for these types of concrete, caution should be exercised when interpreting the results. Emphasis should be placed on controlling the W/B ratio, not slump.

What is an intelligent building?

What is an intelligent building?

Can an intelligent building be defined? It is not necessarily a hi-tech, multistorey building; it may be a ‘motivational building’ or a ‘quality built environment’, or perhaps it is better described as a ‘sustainable building’. For the purpose of this discussion the term‘ intelligent building’ will be used and some possible definitions given.

A building which responds to the requirements of its occupants.

The implications of this statement are many and varied. Certainly a variety of views and explanations are possible, each correct in its own right and all incorporating aspects of other views.

The Intelligent Building Institute (IBI) adopted the following definition (GK Communications, 2001):

An intelligent building is one that provides a productive and cost effective environment through the optimization of its four basic elements: systems, structures, services and management and the interrelationship between them. The only characteristic that all intelligent buildings have in common is a structure designed to accommodate change in a convenient, cost effective manner.

By contrast, the European Intelligent Building Group (EIBG, 2001) states:

An intelligent building creates an environment that allows organizations to achieve their business objectives and maximizes the effectiveness of its occupants while at the same time allowing efficient management of resources with minimum life-time costs.

Both definitions point toward similar conclusions but their approach (the effective means to create an environmentally sensitive and productive centre) is different.

Stubbing (1988) limits his definition to ‘a building which totally controls its own environment’. The implication here is that there is an overriding technical mastery of the building.

Lush (1987) takes another perspective focusing on a multi-dimensional view of spatial efficiency, allowing for the inclusion of extrinsic aspects of the building (exterior spaces), and melding them with its intrinsic fabric, functionality, layout and its degree of responsiveness:

An intelligent building would include a situation where the properties of the fabric vary according to the internal and external climates to provide the most efficient and user friendly operation in both energy and aesthetic terms.

The demand for intelligent buildings

The demand for intelligent buildings

There are a number of factors behind the increasing demand for buildings that may be described as ‘intelligent’ and they reflect not only significant advances in technology but changing attitudes to work and the workplace.

What do people want?

Demand for intelligent buildings and intelligent office space has been driven by clients looking for energy savings, a need for increased worker productivity, and the expectation of a healthier work environment. Tenants want greater utility of floor space. They are factoring in the impact (cost) of restructuring space as the organization restructures to either match market demands or match new organizational forms that aid in establishing a competitive advantage.

The results indicate that people want a greater influence on the environmental controls and spatial layout of the workplace. Indicates that this does not necessarily mean more complexity and greater control but rather that the processes that govern the effectiveness of the workplace be more intuitive. For the intelligent building, this has meant greater distribution of systems and hence a greater need for integration and intelligence, creating or demanding systems that are capable of managing the complexity and range of attributes effectively, without impacting on the functionality of the building or reducing the building’s capabilities.

Precast Concrete Applications

Precast Concrete Applications

Precast concrete has been used extensively in recent years. We have already discussed the advantages to this type of repair process. Here are some of the types of concrete structures where precast concrete can be used:

 ■    Navigation locks

■    Dams

■    Channels

■    Floodwalls

■    Levees

■    Coastal structures

■    Marine structures

■    Bridges

■    Culverts

■    Tunnels

■    Retaining walls

■    Noise barriers

■    Highway pavement