Concrete can be re-used as an aggregate source by crushing it to a

specific size, then adding about 22% flyash 78% portland cement to the

crushed materials to make an alkali-silica reativity resistant concrete mixture.

The Flyash is a byproduct of coal fired power plants.

Thanks Micheal. different aggregates have been used to achieve lightweight concrete. is there a table to show the strength of the concrete with various aggregates in comparison to the strength of normal concrete?

thanks

The strength of concrete is primarily controlled by the water to

cement ratio ( W/C). By using a high range water reducer and keeping

the concrete W/C in the range of 0.34, any good clean aggregate will

do.

Some lighter aggregates would be pumice, vessicular basalt, expanded shale.

If you live in a cold climate, an air entraining agent is needed.

Light weight aggregates work well in warmer climates, or inside buildings that

are not subject to freeze-thaw cycles.

The secret to good quality concrete is a low W/C, and vibrators to consolidate

the concrete to eliminate air voids and get the best particle to particle contact.

Girder Manufactures in the US can achieve strengths between 8,000 PSI,

and 13,000 PSI concrete by using a low W/C and a high percentage of

cement ( 8 sack mixes ), and by curing in steam to maintain temperature

overnight so the concrete can not shrink until it is already strong. They use

very small aggregates ( less than 1/4 inch ) so there is a lot more surface area

of aggregate to cover, thus the 8 sacks of cement per cubic yard.

Remember that light weight aggregates have more surface area to cover

so they require more Portland cement to do the covering of the aggregate.

They also are full of holes so they store water which is subject to

very high expansive forces when it freezes.

thanks Michael for your informative insight

i appreciate your point on the low water to cement ratio for good quality concrete

i am particularly interested in your discussion on light-weight aggregates

the topic of my thesis is "innovative approach to sustainable development of prefab housing".

I am analyzing various building materials (focus on concrete) scoring them from 1-10 under the following headings in order to carry out a comparative analysis -

DESIGN QUALITIES - Level of flexibility and versatility

(There should be various ways the building material can be used when Architects and Engineers are designing)

ENVIRONMENTAL IMPACT - Level of “greenness”

(How environmentally friendly is the building material on the eco-system? )

AIR QUALITY – level of impact on human health with proper ventilation

(How toxic is the building material to living creatures?)

THERMAL COMFORT – Level of resistance to heat load

(How resistant is the building material to heat)

NATURAL LIGHT – level of natural light enhancement

(Does the building material enhance quality light for comfort and power efficiency?)

WATER CYCLE – enhancement of water cycle

(Does the building material enhance reuse of water?)

EFFICIENCY OF USE - Level of efficient usage and availability

(Can the building material be used with appropriate technology and readily available in Nigeria?)

WASTE USAGE– Level of efficient re-usage

(Does generate unusable waste?)

DURABILITY – Level of resistance to climate and usage

(Is the building material resistant to corrosion, wear and tear, warping, fading, leaking and tropical ocean-salty climate?)

FEEDBACK - Level of affordability and cultural acceptability

(Do people like the building material?)

i am currently studying two research papers by Prof Funso Falade -

1- an overview of foamed aerated concrete - a building and civil engineering construction material

2- behaviour of lightweight concrete containing periwinkle shells at elevated temperature

I always wanted to use styro-foam beads and concrete together in

construction panels, but the high difference in density of the two materials

would lead to segregation. perhaps it could be mixed and sprayed

onto a mold, or, sprayed into a mold to make a construction panel with some

insulating properties, moderate strength, and ability to to take screws and nails.

maybe they could have tongue and groove edges so panels could be joined

together easily.

Perhaps the panels could be used for house walls by digging a trench,

sticking them in the ground, joined together, back filling around the edges,

then glue on a complete roof made of the same materials.

I understand that termites are quite a problem in some countries, perhaps they would not like to eat, concrete and styro-foam panel walls buried in the

soils about 3 feet deep. You could make the inside higher than the outside,

and have raised sills at the door ways to step up and over.

Worth a thought.

a brilliant thought Michael

we are designing the first green housing estate in Nigeria

i would like to experiment with different building materials when we get to the construction stage

i will give you feedback on the experimental building materials we use in this project

i think it will be quite interesting

please is there any research work that has been done in your university on green prefab housing?

thanks for everything

I doubt that storing heat for the winter months is a necessity in Nigeria,

but having a house that stays several degrees cooler in the hottest part of the day

could be advantageous. Solar powered vent in the roof help reduce heat, or

wind turbine vents could help.

Thick insulating walls, and white surfaces to reflect heat and light.

A very thick insulating roof with a while upper surface would also reflect light and heat

upward.

in addition to your helpful suggestions, we are also exploring the use of large windows in recessed balconies for cross ventilation. the recess provides a transitional area for cool air to move within the building.

for the roof, there are two options we are considering -

1- have a concrete slab roof and place solar panels on it

2- just have solar paneled roof with insulation

there are cost implications and acoustic considerations

fortunately, the humid, moisture-laden wind in Lagos (close to the Atlantic ocean) does not allow wide difference in temperature when compared with the desert-like northern part of Nigeria where temperature difference between day and night is high. they have dry, hot wind.

I always thought that having cool moist air from under a building being drawn

up through the building , and exiting the top would help keep all of it cool.

Before air conditioning allowed us to be foolish in house design, people

had used wide porches with low roofs, numerous windows, and a central

tower type area with louvers on it to exit the hot air.

I also had another idea, make the house substantial enough to have a parapette

wall around the perimeter, and 1.5 meters of soil atop the house, and grow

a small forest above the house for its cooling effects.

The support structure would need to be very substantial, and thus very

expensive, and fixing roof leaks would be very difficult..

It is not currently practical, but if global warming continues, it might become

a possibility for large groups of houses to be constructed all at one time

with this concept utilizing factories to construct numerous identical roof and

column segments that bolt together. Perhaps the roofs could be segments

of a circle, and the supports have window and doorway openings built into

them.

Houses would be standard circular houses with an open central

courtyard, and a double row of shade trees planted above the support columns

atop the roofs.

I wonder if many people would accept living in large diameter circular houses

with forests on the roof?

Michael, you should be an architect - lol

i like your interesting ideas

like you suggested, we have already added a large concrete cantilever for the roof parapet

vegetable roof garden is being considered along the edges of the roof where the concrete parapet wall is so that excess water can drain directly into the rain-water down-pipe

hot air exiting from roof vent is what we use in industrial buildings due to the huge build-up of hot air.

the hot air in residential buildings is not as much as that and we would instead probably have driving rain (common over here) entering the residence

passive cooling through vegetative foliage is also being applied in our landscape architecture for the housing project

your circular house idea shows that you may be a star wars fan like me.

the courtyard concept is what i use in my hospital designs, shopping mall designs and hotel designs.

this helps to bring in natural vegetation, light and air into a building using transitional spaces to create a wonderful experience of space

i wanted to study civil engineering but changed to architecture at the last minute due to my passion for art.

still, i admire engineers as they are the ones that translate ideas into reality

Engineer, I build roads and bridges, well mostly we replace them with

newer designs with longer spans, bigger girders, bigger columns....

deeper caissons, and the cranes used get bigger and bigger.

The biggest one here is 500 tons and takes twelve semi's to bring

in all the parts and counter weights.

As for Star Wars, guilty as charged, I have the original versions and the

Versions with the added scenes, in VHS tapes, and now have several

hundred DVD's .

Humm..... Since high rise structures need to be substantially constructed

anyway, perhaps a circular Hotel complex with a cantilevered Parapet

overhanging roof would support a cooling forest of large trees. The rainfall would

fill a very large cistern below the courtyard which would then be used as a

supply of water for what ever purpose. Perhaps being pumped though

room radiators that absorb excess heat, and re radiate that heat on more roof top

radiators, or have a separate adjacent building with a cooling tower.

Your system would need a filter, and a method to remove acids and bases from

the water. Solar Panels on the adjacent building could supply the power needed to

move the water.

Being in a place that does not freeze, and has abundant water, adds lots of possibilities to using clean de-mineralized water as a heat ex-changer.

A large centralized circular courtyard limits access from the outside, walking distances, distances traveled by cleaning staff. You could design it so that

each floor had its own laundry facility. There would be spiral stair cases from

floor to floor on the inner circle, bad perhaps a multi-story internal growth column

tiered, with all kinds of plants and flowers.

In Cities we have forgotten how to live with plants and animals, and how to

incorporate them into our structures so we can live in a modern manner, and yet still

be able to view and appreciate a Jungle environment. ( except mosquitoes )

your suggestions remind me of the waterfall inside the emirates mall in Dubai

i would like to design a hotel that had an artificial waterfall with the water passing through the building across the entrance porch

then one could incorporate your circular courtyard with vegetation and lovely birds

it would make the hotel stand out from the rest where people can enjoy water, some huge rocks, lovely plants and beautiful friendly birds

i love nature and it reflects how wonderful God is

the water also can act as cooling agent in line with your suggestion

the grand spiral stair can be like a miniature hill enabling one to experience the waterfall from various angles and varying heights

even the sound of the waterfall will have a relaxing effect