Choosing Pipe Materials for Ready Mix Concrete

Pumping of concrete is very common in today’s concreting in relatively less accessible construction site and also concreting in greater elevation. We have discussed about concreting at highest elevation with the power of Putzmeister pump.

Before performing such operation in unbelievable elevation, some tests were conducted to examine capability of pumps and also to evaluate different connections within pumping system. We have to choose a pipe system that is inert i.e. concrete do not react with any constituent of piping system together with less friction resistance.

Sometimes flexible hose of short length is used at discharge end to facilitate placing. With convenience of placing, it produce substantial increase in friction which produce also some loss in pumping head.

On the other hand aluminum pipes produces another forms of problems. We know cement is a potential source of alkali. Aluminum is found to react with alkalies remain in cement. This reaction produce hydrogen gas which is harmful for concrete.

The harm is done by introducing voids, by hydrogen gas, in hardened concrete. We know voids in concrete primarily reduce strength; the impact is low density, high permeable concrete and other susceptibility of deformation of concrete is induced.

Dear reader so what is ideal material for piping system? Dear reader to have answer of these question you have to wait for next post. Please stay with us.

ASTM Specification for Organic Impurities in Fine Aggregate of Concrete

Dear reader we will discuss here about organic content in fine aggregate. We will not include consequence of organic content in concrete, just discuss about ASTM specification for organic contamination in fine aggregate.

We have already learnt about influence of organic content in soil, like this concrete is also subjected to their detrimental effects. The fine aggregates having darker color are suspected to have organic impurities and often many specifier or purchaser rejects them at first sight.

A simple colorimetric test is conducted to determine the quantity of organic content in fine aggregate. We will learn tests that are conducted, as per ASTM standard, for this purpose. But darker color is not due to only organic content; there may have other discrete particles like lignite and coal etc. in small quantities.

Very often these discrete particles render discoloration in sand and code suggested not to reject sand only depending of color. Such sand, failed to pass this test, can be used if it passes Test Method C87 with certain condition.

These are:

When mortar produced with this sand having organic impurities is tested for impact of organic content on strength, produce a relative strength after 7 days varying not less than 95 percent. As discussed above test is done according to C87 (ASTM).

Variance in Shipment of Fine Aggregate for Concrete

Dear reader we are discussing about ASTM specification for fine aggregate for concrete. In case of concrete mix design, the designer assumed some parameter like fineness modulus (as relevant in this post) etc. They assume a fineness modulus for concrete proportioning considering a source of fine aggregate available in desired location.

Now do you think, assumed fineness modulus can be maintained throughout the full shipment for particular grade of concrete for desired member? We know concrete proportioning is changed significantly depending on strength, workability, durability etc.

To explain this topic we have to know about base fineness modulus. We have discussed about fineness modulus, base fineness modulus are determined from former tests, but if there have no data from previous test, it is measured taking average values of fineness modulus of first ten aggregate samples on the sequence. When less than ten samples are tested, average is taken from all preceding fineness modulus values.

Specifier or purchaser continues shipment of desired fine aggregate from a selected source, only when difference between fineness modulus and base fineness modulus is within 0.20. They have authority to reject or approve fine aggregate depending on base fineness modulus.

But when shipment from a source, however, has to continue, depending on difference between two values, suitable adjustment should be conducted in mix proportioning to maintain desired properties of concrete.

Fineness Requirements of Sand for Concrete

Dear reader we have discussed about straight forward limits for fineness of sand used in concrete according to different standards of the world. Here we like to explain some additional requirements except fineness.

Dear reader we have learnt about limits of fineness modulus according to AASTHO and ASTM. These values were between (2.3-3.1). But if aggregate do not meet these requirements what should be done? Should it be considered as unusable? We will find this answer in next paragraph.

The fine aggregate that don’t meet this requirements can be used if we have some data about the concrete produced with this aggregate can be accepted of –

First option,

Concrete produced with identical fine aggregate collected from same source, produce acceptable performance in identical concrete construction. 

Second option,

Concrete of the type specified, produced with desired fine aggregates, should posses relevant properties (that properties, important for particular application, we considered) at least become equal to that of concrete having same constituents, having exception that fine aggregate that is referenced should be collected form source that have acceptable performance report identical concrete construction.

We have discussed about fineness modulus above but other requirements that have to meet are:

1. Less than or equal to 45% of fine aggregate should not pass through any standard sieve.

2. Similar equal percentage of fines should not retain on two consecutive sieves.

Identifying Concrete Cracks from Appearance

Dear reader we have discussed many aspects of cracks in concrete. Plastic shrinkage cracks micro cracks, cracks due to alkali silica reaction, cracks due to yielding of reinforcement and other cracking agent, crack and corrosion friendly environment were discussed. Here we will show cracks in structural members. Here we will include cracks beam and column. 

Cracks in concrete member due to Diagonal shear: 

Cracks in concrete member due to Shrinkage cracks

 Cracks in concrete member due to Flexure (Bending )

 Cracks in concrete member due to Bond

Cracks in concrete member due to Buckling of steel (compression steel):

Cracks in concrete member due to failure of stirrups, resulting buckling of longitudinal steel or steel corrosion.

 Cracks in concrete member at about to reach its ultimate loading