Civil Engineering - Building Materials - Discussion

These are provided along the transverse direction to allow the expansion and contraction of a concrete slab due to temperature and subgrade moisture variation.

They are intended to prevent potentially damaging forces accumulating within the slab itself or surrounding structures. Maximum spacing of expansion joints ranges from 25-27 m in jointed reinforced concrete slabs and from 40 m (for slabs <230 mm thick) to 60 m (for slabs >230 mm thick) in unreinforced concrete.

Good, thanks for explaining @Adebola.

Anyone can Explain the limits of expansion joints for different structures?

The dry sand and the sand completely flooded with water, have practically the same volume, at initial stage of adding water to a measure of dry sand, the sand bulks that is increasing in volume but this increase doesn't continue indefinitely, bulking in sand depends on the % of moisture, up to 5% of moisture makes the sand bulk greatly. At a certain % of moisture content, the bulking cases and the volume of the moistened sand begins to decrease. Experiments have shown that when all the voids in the sand are filled with water about 14% moisture (sand saturated with water) its volume practically becomes equal to the measure of dry sand.

The bulking of sand which is the process by which sand increases in volume as a result of the presence of moisture content must be taken into account while proportioning of the aggregate. Moistened sand bulks greatly and increases in volume hence for each measure of moistened sand, the actual volume of sand particles becomes exaggerated so more sand should be taken to take care of bulking else the mix will be undersanded.

The bulking of sand should be taken into account when volumetric proportioning of the aggregates is adopted. Otherwise, less quantity of concrete per bag of cement will be produced, which naturally will increase the cost of concrete. Also, there will be less quantity of line aggregate in the concrete mix which may make the concrete difficult to place.

When moisture content is increased by adding more water, the sand particles pack near each other and the amount of bulking of sand is decreased. Thus the dry sand and the sand completely flooded with water have practically the same volume.

No, it's 20m for conc. And 45 for rcc.

Same thing that concrete structure have expansion joint when the length is increased 45 m.

"The dry sand and the sand completely flooded with water, have practically the same volume".

How can this happen?