Concrete Defects 5

[dik]

Is there a standard that quantifies defects? For example, is there a publication that defines what a 'bug hole' is? or the distinction between bugholes and segregation or honeycombing? or for that matter, what constitutes honeycombing/segregation?

Dik

 

[DTGT2002]

This is a fun one with no overwhelmingly concise answers. However, reviewing the following documents may help in understanding.

ACI 201.1R-92 Guide for Making a Condition Survey of Concrete in Service
ACI 309R-05 Guide for Consolidation of Concrete
ACI 309.2R-98 Indentification and Control of Visible Effects of Consolidation on Formed Concrete Surfaces
ACI 347-04 Guide to Formwork for Concrete

Please note that these documents are guides and not codes. As such, they are to provide information and best practice, but as they are not written in mandatory language, they cannot be simply references for inclusion in specs or the like without being re-written in mandatory language.

The "D" word you list above (defect) presents a challenge for defining and everyone has an opinion.

From where I stand, a bughole is not a defect, while segregation and honeycomb may have a structural implication and must be reviewed to determine if a structural "defect" exists.

Of course, defect also must be reviewed in light of the specs and non-structural "defects" could include concrete that deviates from a noted finish.

All of that said, bugholes are nearly impossible to eliminate though good practices can minimiz thier appearance. And, no, not even the best contractor can guarantee the uniform appearance of bugholes or air voids.

Hope it helps,

Daniel Toon

 

[Ron]

Dik,
Each of those terms is defined in ACI SP-19 "Cement and Concrete Terminology" and in ACI 116 "Cement and Concrete Terminology".

[highlight]bug holes (also known as surface air voids)[/highlight]—small regular or irregular cavities, usually not exceeding 15 mm in diameter, resulting from entrapment of air bubbles in the surface of formed concrete during placement and consolidation.

[highlight]honeycomb[/highlight]—voids left in concrete due to failure of the mortar to effectively fill the spaces among coarse-aggregate particles.

[highlight]segregation[/highlight]—the differential concentration of the components of mixed concrete, aggregate, or the like, resulting in nonuniform proportions in the mass. (See also bleeding and separation.)

[highlight]bleeding[/highlight]—the autogenous flow of mixing water within, or its emergence from, newly placed concrete or mortar; caused by the settlement of the solid materials within the mass; also called water gain.

[highlight]separation[/highlight]—the tendency, as concrete is caused to pass from the unconfined ends of chutes or conveyor belts or similar arrangements, for coarse aggregate to separate from the concrete and accumulate at one side; the tendency, as processed aggregate leaves the ends of conveyor belts, chutes, or similar devices with confining sides, for the larger aggregate to separate from the mass and accumulate at one side; or the tendency for the solids to separate from the water by gravitational settlement.

Ron

 

[cvg]

USACE
EM 1110-2-2002 Evaluation And Repair of Concrete Structures

 

[dik]

Is there any reference to the extent or the area involved?

Dik

 

[DTGT2002]

Are you asking in reference to what area should be repaired when honeycomb is encountered or what?

 

[beton1]

I had a similar? thread under concrete engineering, general discussion, back in early April, I believe.
I also found ASCC (American Society of Concrete Contractors) has "position" statements on such issues.
Another perspective, in pretty plain terms. I had to mediate a dispute of 'what is a defect' in walls for a commercial plaza/big box complex. A very subjective matter (often without specs); peoples expectations are different. Someone wants to pay for structural concrete but expects a architectural or 'superior' quality finish. Mix design is obviously a big factor on what can realistically be achieved.

 

[DTGT2002]

And many folks simply want to paint an as cast concrete wall and expect it to look like drywall. Not gonna happen unless the drywall you have to compare it to has been in the same room as a teenager and a bb gun.

 

[BigH]

Ron - bug holes - what we call vugs in Toronto??

 

[dik]

DTGT2002... these 'bug holes' are approx 1-1/2" dia and are also located within the concrete matrix. The purpose of the concrete from a durability point would be slightly less than critical.

Dik

 

[Ron]

BigH..Yes...vugs or vuggy usually refers to geology, but same result in concrete-a void or series of voids....haven't heard that one since my Trow days.

 

[DTGT2002]

dik,

Without seeing a picture or the area in person, I would hazard to say that description extends beyond a bughole.

I would not expect to repair a bughole, but if you have voids throughout the depth of the member, it certainly seems a structural defect would be evident.

Are there voids around reinforcing steel? Is the cover reduced over a substantial area - larger than the 15mm diameter referenced?

From your description of voids extending into the concrete matrix, I would get the feeling there are more than just surface effects.

 

[dik]

I don't have pictures of the voids, but, I understand that they extend partway into the matrix. The surfacial 'bugholes' are as large as 1-1/2" as noted (40 mm). Coring into the area where there are surfacial defects located other air voids below the surface. The affected area could be 1000 sq.ft. (100 sq.m.)

On another thread, is there a measuring device that can readily locate sub surface voids? The device should be small, portable and relatively simple/inexpensive to use.

Dik

 

[DTGT2002]

A grid of ultrasonic pulse emitters and receivers could be used if both sides of the affected area are accessable, but trained operators are needed and while the individual sensors are small and portable, the test grid and not simple or inexpensive to use.

Basically, voids cause a longer reading when compared to a reference sample of sound, like concrete.

Chipping outside the confining ties or bands could be done to expose other near surface pockets, but it can be challenging.

I am assuming the voids exposed in the coring would qualify as a structural defect and an investigation is in order to determine the extent of the defects. Have any friendly testing companies with ideas or who are willing to discuss options?

 

[dik]

DTGT2002
Access is from one side only.
Dik

 

[Zambo]

Ultrasonic may be possible. I have used for cracks in pre-stressed concrete and access from one side is acceptable. Not sure if this technique works with voids and to what depth.

 

[dik]

Thanks Zambo, I'll try chasing down some info on this.

Dik

 

[Ron]

Dik,
I've done a lot of pulse velocity UT on concrete. Voids tend to disperse the wave. If you shoot straight through the concrete section, and you know the approximate velocity of the wave through the concrete, you can determine an "equivalent" thickness. If you compare that to the actual thickness, it will tell you if you have voids in that cross section, but it won't tell you where the voids are located or if it is one large void or numerous small voids.

Ron

 

[dik]

Thanks, Ron. The concrete is several feet thick. Would the wave 'reflect' from the void surface?

Dik

 

[Ron]

Dik,
If the transmitter is on the side of the voids, dispersion will happen, but because of the relative size of the voids compared to the thickness, you might not be able to pick up void evidence. If the transmitter is opposite the voids, you probably won't notice any void characteristics, again due to the size of the voids, relative to the thickness of the concrete.

Impact Echo is another method that could be used, but again, I think all are limited in their ability to "see" small voids relative to thick concrete. Impact Echo is less so, since it is a "one-side" method, as compared to PV which requires access to both sides of the concrete (there are some exceptions, but generally that's the case).

If your issue is critical, you might contact Olson Engineering in Colorado. They make equipment and provide consulting for such.

Good luck.
Ron