The science behind
The technology and electronics implemented in the CBV vehicles has been developed according to main international standards providing an integrated system that leads the operator to reduce human errors and respect the three “pillars” of concrete performance :
- compressive strength
- fresh-state workabilit
Mix design of Concrete
The approximate formulation of 1 m3 of concrete is reported in the picture above, but of course it may vary depending on the specific characteristics of the materials used (e.g. shape, density and grain size distribution of aggregates) and on the specific performance required to concrete (workability, strength, etc.). For this reason, when a new concrete formulation must be set-up, mix design methods can be very helpful. Starting from the characteristics of the single components (cement, aggregates, etc.) and the desired characteristics of the final concrete, these methods allow to outline an approximate concrete receipt.
For the manufacturing of a good quality structural concrete, the amount of the single components must be measured with suitable accuracy. Materials can be measured by mass or (according to some standards) by volume. National and international standards fix the tolerances to be respected in the measurement of cement, water, aggregates and chemical admixtures. The moisture of aggregates must be taken into account too.
Mixing must be efficient, i.e. give a homogeneous material in reasonably short time. A too prolonged mixing may lead to several problems, such as air entraining (and, hence, strength decrease). Moreover, mixing cannot delay setting, as hydration nevertheless occurs : conversely it might destroy the newly formed hydrated compounds. During too prolonged mixing, water is always added in order to maintain some fluidity, but it is extremely harmful for final compressive strength.
Workability of concrete
Workability is meant as the ability of fresh concrete to flow and properly fill the formworks. Workability is measured by the slump cone (also known as Abrams cone), according to a standard testing procedure (slump test). Slump greatly decreases with time (especially in hot climate), due to concrete setting, hence the required fluidity must be ensured at the moment of casting.