Poured Concrete Slab Scopes of Work

bulgefetaΠολεοδομικά Έργα

29 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

73 εμφανίσεις


Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

Poured Concrete Slab

Scopes of Work

G
ENERAL
I
NTRODUCTION TO
P
OURED
C
ONCRETE
S
LABS


Poured concrete slab construction is an important element of high performance
home construction. Either serving as a slab
-
on
-
grade foundation, or as a
basement or crawlspac
e floor, the slab plays a critical element in controlling
moisture in the home as well as keeping pests and even gases such as radon,
out of the indoor environment. High performance home slab construction
integrates proper site preparation with proper sea
ling and insulation with
concrete mixtures that increase strength and slab designs that allow for
controlled predictable cracking.



Poured Concrete Slabs Inside Residential
Buildings

(Basements or Crawl Spaces)

I
NTRODUCTION

The material presented here i
s applicable in most cases, for finished or
unfinished basements, or for conditioned or vented crawl
spaces (see Figure 3
and Figure 4).

Attention to these details plays a critical role in the performance
and longevity of the slab and the indoor environme
ntal quality.

Purpose of this High Performance Scope of Work

The High Performance Scopes of Work for Concrete Slabs trade contractor is
designed to achieve the following:



Proper preparation of slab area and proper installation of concrete slab
material
s,



Facilitate and assure coordination of mechanicals and other trades’ work
beneath and through the slab,



Assure specified quality and quantity of materials are provided and
utilized, and



Achieve agreement in advance between builder and trade contractor of

job ready and job complete criteria.


Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

The scope defines the design and construction specifications that must be
addressed in order to construct a high performance slab. This scope addresses
the following key design and construction specifications:

o

Concret
e mix (to achieve the design strength of the concrete)

o

Pouring and working of concrete (to assure uniform strength, finish,
and durability)

o

Curing procedures, especially for very hot and very cold conditions
(proper curing of concrete improves concrete dur
ability)

o

Control joints (to avoid unacceptable and excessive cracking of
concrete)



Defining the expected work of the contractor such that roles and
responsibilities of contractor and builder are clearly understood and both
may be accountable for required
performance.



Defining the conditions required for commencement of each contractor’s
work (job ready checklists, one to begin preparation of slab area, and one
to start concrete pour/finish operations).



Defining the conditions required for acceptance of eac
h contractor’s
completed work (job complete checklist, after pouring concrete, removing
forms and cleaning the jobsite).

Scope Content

This poured concrete slab Scope of Work covers the following residential
installations: Concrete slab between C.M.U. o
r concrete walls, by others (
See
Figures 3 and 4);


The Scope is organized so that it can be downloaded by designers, builders or
trade contactors from the Internet by the section of interest to them. As a result,
some information is intentionally repeate
d in different sections of the Scope since
it applies to both the design and the construction stage.

Any high performance home Scope of Work assumes certain field activities and
an order of work. While these assumptions are not an integral part of the
bui
lder/trade contractor legal contract, these assumptions can make a useful
training aide or become the basis for a field manager’s checklist. (See
Assumed
order of work
.)


Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.


Figure
1
: Foundation Section


Concrete with Interior Sla
b



Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.


Figure
2
: Foundation Section


CMU with Interior Slab

Builders Challenge

The Builders Challenge certification program is used to confirm that certified
homes are designed to achieve at least a minimum level of energy perform
ance
that exceeds current efficiency requirements by 30% and to document their as
-
built performance levels, even including net
-
zero energy homes (ZEH). In
addition to the energy performance requirement of the Builders Challenge, there
is a set of
Builders Challenge Quality Criteria

(BCQC) representing high
performance home best practices. The complete set of BCQC requirements and
the Builders Challenge Qualit
y Criteria Support Document can be found at:
Builders Challenge Quality Criteria Support Document
.

A builder may also use the Scope of Work to v
erify that the Builders Challenge
criteria relevant to each trade contractor have or have not been completed by
each of their trade partners. Builders Challenge items are indicated throughout
the scopes of work and checklists.
They are denoted by a gray
highlight.

In
addition, a note in italics accompanies the provision noting which Builders
Challenge Quality Criteria the item addresses. For example,
[BCQC
-
2]

stands
for Builders Challenge Quality Criteria item number 2.

Concrete As A Material

Causes

of Surface (non
-
structural) Damage

Applied chemicals and natural elements can deteriorate the surface of
concrete. Surface defects such as flaking, scaling, or spalling may also be
caused by improper finishing. Excessive powdering or chalking may occur

Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

d
ue to improper troweling, excess water, or when uncured concrete is allowed
to freeze.

Concrete Performance Defects

(specific limits are included in trade
contract)

Concrete defects are defined as follows:

1.

Horizontal displacement of any part of the concr
ete slab in excess of 3/16”

2.

Voids in the concrete that expose any portion of the reinforcing steel or
reinforcing steel mesh

3.

Loose, missing, or crumbling surface material larger than 1 square inch

4.

Cracks in excess of 3/16” wide and longer than 2 inches in
length

A
vailable Performance Tests

As required by the builder, contract language can require that the trade
contractor agree that full compliance with this Scope of Work requires
demonstrating that the completed work meets the builder’s requirements using

the following tests:

Performance Test 1:

Slump tests during any concrete pour operation


ASTM
standard slump tests
1

will be completed and evaluated on
-
site by the Builder’s
engineering consultant. Concrete slump during any pour shall be between 3
-
5
inc
hes.


Performance Test 2:


Compressive strength of concrete


Three concrete
cylinder samples will be prepared
2

by the Builder’s engineering consultant as
directed by the Builder from each concrete order. Additional samples may be
made from any continuous

pour exceeding 50 cubic yards.




Compression test samples (cylinders) will be removed from the jobsite
after 48 hours by the Builder’s engineering consultant.




Trade Contractor is to protect cylinders from movement or damage until
removed.



Testing of all
cylinders will be conducted in accordance with ASTM C873
-
04 after 7 days and after 28 days. Tested compressive concrete strength
must exceed 70% of specified psi after 7 days, and at least 3000 psi (or as
required by local code) after 28 days. One cylind
er from each sample will
be maintained by the testing lab as a backup.

The two concrete slab scopes of work included here include a version of this
performance language.




1

Refer to
ASTM C143 / C143M
-
09
for slump test specifications

2

http://nrmca.org/aboutconcrete/cips/34p.pdf



Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

D
ESIGN AND
S
PECIFICATION
P
REREQUISITES

Slabs Within the Interior of a Residential Buil
ding

Concrete is a material requiring careful attention and specifications to the design
assumptions. Below is a summary of some important issues and assumptions to
keep in mind during the design and plan development phase of any project.

Design Assumptio
ns, Goals and Parameters



A quality and durable result is dependent on material quality and workmanship
quality, and adherence to the project specifications.



Slabs are designed and constructed to allow for controlled cracking and
expansion.



Based on EPA
and building code radon exposure maps
(
http://www.epa.gov/radon/zonemap.html
), naturally occurring gas in the
ground can be expected to move through cracks in the slab into the living
space unless a ne
gative sub
-
slab pressure is maintained.



Concrete mixtures are designed and used to allow for proper curing resulting
in maximum strength and quality of the final product. See “Hot and Cold
Weather Installation and Curing Requirements”

sections.



Guidance

on control joints includes details on expansion joint material and
control joints, maximum distance of 10’ between control joints for 5” slabs with
¾” maximum aggregate size, and detailing of construction joints (stopping
places or cold joints).
3




Careful

control of the quality of the concrete delivered to the jobsite is
assumed in the design, including:



Concrete placement,



Finishing, and



Curing (Cold and hot weather installation notes and curing guidelines are
to be reviewed by to the builder’s contract
officer for inclusion in
concrete slab trade contracts as needed.)



All interior concrete flatwork shall have a minimum compressive strength of
3000 psi at the end of 28 days.



Minimum code required slab thickness for a fully supported concrete slab are
spec
ified. A fully supported slab, by definition, is supported at all edges by a
structural wall or turned
-
down footing and rests on original ground or
compacted clean fill. (See Figures 1 and 2)



A drainage layer under the slab provides a capillary break to p
revent migration
of liquid water though the slab and into the conditioned living space.




3

http://www.cement.org/tech/faq_joints.asp




Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.



Original undisturbed soil or clean fill compacted to a minimum of 95% of the
California Bearing Ratio at 80% moisture content fully supports the slab.



Prepared properly
, the concrete slab area base is to support the slab and
assist in alleviating/minimizing moisture problems.



A continuous vapor retarder with joints overlapped a minimum of 12” is
installed in contact with the underside of the slab. (BCQC
-
2)



Foundation
and structural concrete is expected to maintain its integrity
throughout the life expectancy of the building. Poured concrete shall not crack
in excess of 3/16 inch in vertical or horizontal displacement. Concrete should
not pit, scale, or spall to the ext
ent that the aggregate is exposed under
normal weathering and use.



Water is not to be added to the ready
-
mix truck at the site. Additional water in
the mix weakens the concrete! The delivery truck driver must not add water to
the concrete while in the del
ivery truck. The concrete delivery company has
the responsibility for control of the concrete slump to meet the project
specifications until placement in the forms.



The quality of concrete is directly dependent on the ratio of water to the
cement in the m
ix. The higher the ratio, the weaker the concrete. A mix that
meets the project specifications is crucial to long
-
lasting durable concrete. The
amount of water added on the site must be carefully monitored. The slump
shall be maintained between 3
-
5 inches.



Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

Cold Weather Installation
a
nd Curing Requirements

Provide to the builder’s contract officer for inclusion in all concrete slab
trade contracts

Concrete poured in cold weather requires special care to allow the concrete mix
to properly achieve its design

strength without freezing. Cold weather is defined
as any time concrete will be installed with air temperatures at the site 35 Degrees
F and falling. Cold weather also includes any time air temperatures are below
freezing for a period of 7 days after in
stallation.



Any time air temperatures are below 40 degrees Fahrenheit (F), the water and
aggregate should be heated by the ready
-
mix plant so that the mixed concrete
is placed at a temperature between 50 and 70 degrees F.



Refuse delivery of concrete that

is too wet. A standard slump test is used on
each load to verify that the concrete delivered has the design water cement
ratio.



No concrete is to be poured on frozen ground.



To ensure maximum strength, the new concrete surface should be protected
from
rapid drying by covering with polyethylene for the first 24 hours after
finishing.



New concrete can be insulated from cold weather by maintaining blanket
-
type
material (insulation batts, straw, hay, grass) or fiber filled bags of low density,
lightweight
material.



New concrete can be protected from freezing by enclosing (or closing in) the
space over the concrete slab and providing temporary heat.



Any direct vent heaters are not to be used to blow hot air directly on new
concrete and are to be used in an a
djacent area to warm the entire space.
Non
-
direct vent heaters can be used inside the basement, garage, crawl
space, or stoop areas. Non
-
direct heaters must be on a non
-
combustible
surface and not in direct contact with new concrete. The concrete contract
or
may cut the hole for venting through the exterior wall using a hole saw. Attach
the cut
-
out material to the wall for later replacement. Electrical cords are not
to be run through windows or doors but only through such cut
-
out holes



Forms should be left
in place for at least 24 hours after concrete placement to
protect the new concrete from freezing. Only approved concrete additives and
curing practices may be used. Accelerators shorten the set time of concrete,
allowing a cold
-
weather pour, early remova
l of forms, early surface finishing,
and in some cases, early load application. Proper care must be taken while
choosing the type and proportion of accelerators, as under most conditions,
commonly used accelerators cause an increase in the drying shrinkage

of
concrete.

Note: Calcium chloride is a common accelerator, used to accelerate the
time of set and the rate of strength gain. It is only to be used if it meets the

Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

requirements of ASTM D 98. Excessive amounts of calcium chloride in
concrete mix may resu
lt in rapid stiffening, increase in drying shrinkage
and corrosion of reinforcement. In colder climates, calcium chloride should
not be used as an anti
-
freeze. A large amount of calcium chloride is
required to lower the freezing point of the concrete, whic
h may ruin the
concrete.
4




4

http://www.toolbase.org/Techinventory/TechDetails.aspx?ContentDeta
ilID=693&BucketID=6&CategoryID=5




Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

Hot Weather Installation And Curing Requirements

Provide to the builder’s contract officer for inclusion in concrete slab trade
contracts

Concrete poured in hot weather requires special care to allow the concrete mix to
properly
achieve its design strength without excessive non
-
structural surface
cracking. Hot weather is defined as any time concrete will be installed with air
temperatures at the site 90 Degrees F and rising plus periods of direct sun for the
first 48 hours after
concrete finishing.



Refuse delivery of concrete that is too wet. A standard slump test is used on
each load to verify that the concrete delivered has the design water cement
ratio.



Do not add water to the ready
-
mix truck at the site. Additional water
in the mix
weakens the concrete! The delivery truck driver must not add water to the
concrete while in the delivery truck. Control of the concrete slump to meet the
project specifications until placement in the forms is the responsibility of the
delivery
company.



During hot weather, the internal heat of hydration will add to the hot weather
temperatures to accelerate the concrete setting time resulting in difficulty in
achieving the desired on
-
site finish. If not managed, accelerated setting times
will al
so result in excessive non
-
structural surface cracking. Retarding
admixtures can slow down the concrete set in hot weather and allow the
concrete contractor time to properly finish the new concrete.

“Retarding admixtures slow down the hydration of cement
, lengthening set
time. Retarders are beneficially used in hot weather conditions in order to
overcome accelerating effects of higher temperatures and large masses of
concrete on concrete setting time. Because most retarders also act as
water reducers, the
y are frequently called water
-
reducing retarders. As per
chemical admixture classification by ASTM
-
ASTM C 494, type B is simply
a retarding admixture, while type D is both retarding and water reducing,
resulting in concrete with greater compressive strengt
h because of the
lower water
-
cement ratio.


Retarding admixtures consist of both organic and inorganic agents.
Organic retardants include unrefined calcium, sodium, NH4, salts of
lignosulfonic acids, hydrocarboxylic acids, and carbohydrates. Inorganic
ret
ardants include oxides of lead and zinc, phosphates, magnesium salts,
fluorates and borates. As an example of a retardant's effects on concrete
properties, lignosulfate acids and hydroxylated carboxylic acids slow the
initial setting time by at least an ho
ur and no more than three hours when
used at 65 to 100 degrees Fahrenheit. The concrete contractor, however,
need not memorize these chemical
-
specific results. Given the specific job

Disclaimer

Neither the NAHB Research Center, Inc., nor any person acting on its behalf, makes any warranty, express or implied,
with respect to the use of any information, apparatus, method, or process disclosed in this publication or th
at such use
may not infringe privately owned rights, or assumes any liabilities with respect to the use of, or for damages resulting from

the use of, any information, apparatus, method or process disclosed in this publication, or is responsible for stateme
nts
made or opinions expressed by individual authors
.

requirements and goals, the concrete supplier should offer appropriate
ad
mixtures and concrete mixes from which to choose.”
5



To ensure maximum strength, the new concrete surface should be protected
from rapid surface drying by covering with polyethylene for the first 24 hours
after finishing, covered with a standing layer of wa
ter, damp burlap, or
repeatedly sprayed with water.





5

http://www.toolbase.org/Techinventory/TechDetails.aspx?ContentDetailID=693&BucketID=6&CategoryID=5