So first; what is the difference between lime and OPC? They are both calcined limestone(limestone that is heated to drive off CO2) often with other stones like shale and clay, but OPC is heated to a much higher temp(2700F) and left in the kiln significantly longer for the same type of limestone. This is very energy intensive, so OPC accounts for 5-10% of all anthropogenic CO2 emissions and is expected to increase another 50% by 2020.
From The Guardian:
The trouble is, a modern cement kiln is, for the wider environment, the equivalent of having a cigarette permanently at your lips. Not only do modern plants consume as much energy as a small town; the kilns exhale clouds of toxic organic chemicals, such as dioxins and furans and various, possibly life-threatening, hydrocarbon compounds.
Acid gases generated by the immense heat of the combustion process, billow into the atmosphere, adding a further raft of heavy metals - lead, mercury, cadmium, chromium - to the toxic curl. These pollutants spewing from the stacks are joined by large amounts of dust and gas from the plant operations; and cement mixers guzzle a lot of petrol.
It is a filthy brew, redolent of what has gone wrong with industrialisation: environmentally and financially expensive and linked in several medical reports to the aggravation of lung complaints, especially asthma or emphysema. It is, however, the necessary price we continue to pay to progress in this late industrial age.
Besides the heavy environmental impact of OPC, there is the issue of durability. Often these concretes are degraded and replaced in only 50 years, while Roman structures built from natural concrete are in good condition after 2000+ years.
So, why is OPC in such heavy use worldwide? It is quick and easy. I can't see any other reason for it's popularity.
Lime based concretes require much longer setting times and don't achieve early strength and water resistance like OPC concrete. They also take more skill in mixing and setting, so laborers with little experience like the ones typically used for OPC concrete can not be used and job costs increase.
Tomorrow I will post the chemistry of concrete and what can be done to limit OPC use and extend the life of OPC concretes.
Each concrete type may have additional requirements at the wall-to slab joint depending on it's bending capability, another property. Code requires #3-4 (1/2") rebar @ 24 inch centers for expansion joints and monolithic. Frost Protect Shallow Foundations are another topic, I don't subscribe to the foam insulation especially it's lack of compression, deflection/creep property compared to concrete that has higher values....some try and compare/justify foam to soil "bearing" property which is a mistake. Fiber reinforced MGO would be a great slab/wall/roof if one could get it approved and installed at reasonable cost.
I tired to get my inspection office and ready mix companies (around 5) to consider other cements but, they need these properties by third part testing, ICC letter, or code, and high volume sales to even consider it, I as one production home builder is not enough. The big reason OPC is so popular is low cost for high strength. You can obtain compression values on 4-6" thicknesses of 10-15,000 KSI by increasing the ratio of OPC to aggregate. Magnesium cements will double or triple that at half the thickness, light burnt @ ~800F kiln temps but, the only USA company mining it is Premier and it is over twice the cost of OPC, leaving shipping and carbon foot print from China behind. If we have to ship in or run our own generators to mix on site we just defeated the purpose of not supporting the OPC factory. In all fairness to OPC foot prints we have to look at where those plants are with respect to others like lime, shipping pollution, and total embodied energy that will vary on location. High temp/pressure cures also produce stronger fibers such as carbon, e-s glass, aramids, basalt, polymers, used to reinforce concretes which is another way to reduce the amount of OPC, but making them also generates a carbon foot print and some like basalt raw material fiber are shipped in from China or Russia(furnace temps around 350 degree the type of furnace needed is in China/Russia), glass too, if, you can get the ACI code past inspection, and, a ready mix company offers it. The issues with these are they are coated in plastic matrix usually epoxy and if you've read this site enough we know what plastics do to breathability. Planer fiber mesh and rebar is another, or a hybrid of continuous and chopped fibers (FRPs) is what large commercial building's use. Code does not require steel but does require it can take the loads as proven by R401.2
Code requires a min width of 12" for soil bearings 1500 PSF + 1-2 stories. Fastener coatings also has to be looked at....MGO does not like galvanized. I believe nor does lime IIRC so people prime them. Anchor bolts can also be cad plated, and the concrete has to show it can take the pull out strength per diameter and spacing, seismic and wind dynamic loads per building height. I do not see a material requirement for fasteners in code, only that we have to proove it can take the loads per R401.2
My biggest issues with OPC and steel is they are thermally and electrically conductive, corrode, crack, emit pollutants and small particles to indoor air....even epoxy coated steel rebar wears over time as does galvanized. Fiber (carbon, corrosion resistant e-glass(ECR), silicate coated basalt) matrix bonds are much stronger and non-conductive as is MGO. Stainless would be another good cement reducer but too costly.
The latest NASA satellite data last year shows drastic improvements in OAQ (Outdoor Air Quality). Automobiles are the biggest contributor, and factories. People may want to reconsider using natural ventilation in some of these areas still. Yes we want to keep up the good work. Midwest-East is the worse, and I thought CA was bad. I remember back in 70's growing up in Pomona Valley, CA we could not go out to recess due to "Smog Alerts" taking deep breaths hurt real bad, that do not exist today.
IRC Code: See CH 4: https://law.resource.org/pub/us/code/ibr/icc.irc.2012.pdf
ACI 318: https://law.resource.org/pub/us/cfr/ibr/001/aci.318.1995.pdf
Terry Ruth wrote: The biggest impact on changing the cost or supply-demand is showing a code prescriptive path for folks to use, or have an Analytical path (approved tested properties per ASTM, ISO) for a licensed PE. Must been nice to live back in the Roman days without all the legal red tape and law suits, liabilities.
The first known building code was written by Hamurabi 4000 years ago. I don't know if it was better, but the law was very clear on building failures.
229. If a builder has built a house for a man, and has not made his work sound, and the house he built has fallen, and caused the death of its owner, that builder shall be put to death.
230. If it is the owner's son that is killed, the builder's son shall be put to death.
231. If it is the slave of the owner that is killed, the builder shall give slave for slave to the owner of the house.
232. If he has caused the loss of goods, he shall render back whatever he has destroyed. Moreover, because he did not make sound the house he built, and it fell, at his own cost he shall rebuild the house that fell.
233. If a builder has built a house for a man, and has not keyed his work, and the wall has fallen, that builder shall make that wall firm at his own expense.
The glue in OPC is called calcium silicate hydrate (CSH), about 75% of the cement powder is converted to CSH, the rest is mostly calcium hydroxide (CH). The CH migrates out of the interstitial matrix of the concrete and leaves behind a network of porosity that can allow water ingress. This weakens the concrete, especially when other compounds enter the concrete like sulfates and chlorides that compromise the concrete and in freezing weather can cause spalling. When the CH reaches the surface of the concrete, it reacts with CO2 and creates CaCO3 as a surface efflorescence. Sulfates can combine with CH to cause sulfate expansion reactions within the concrete, while chloride ingress can cause rusting of metal reinforcements and "rust jacking" another expansive reaction. Silica based aggregates can destroy the bond between the CSH and the aggregate, causing expansion and cracking.
So, if you want OPC concrete to last, you must design a mix that converts all of the cement powder to CSH and not leave any CH to react negatively within the concrete as it ages. The addition of reinforcing materials is beneficial to the long term strength of an OPC slab, but the chemistry is such that without a pozzolan to increase liquid phase cement conversion to CSH, the residual CH will cause the eventual degradation and destruction of the concrete. If you have the right pozzolan and aggregate, it is possible to reduce the amount of OPC added to the mix by 50 - 75%. The initial set strength is lower but long term strength and durability are increased, even with less cement added since 100% of the cement is converted to CSH and there is no residual CH to cause problems.
If OPC is mixed and set properly, it can have a carbon footprint that is near that of a natural cement, especially, as Terry alluded to, when transportation of all components of the concrete are factored in. Though CO2 emission is just one of many factors in an environmental assessment, so don't go thinking OPC is green just yet.
Next post; direct comparisons of natural cement to OPC.
ACI 318 allows tested hydraulic cements or "blended cements" if tested per ASTM C595. Does not allow lime type S or SA as "principle cementing constituent of structural concrete". If you look at the American Lime Association or ASTM testing of the mechanical properties are pretty low since they are not burnt as high. It's good for plaster, walkways perhaps, insulation cement, not high loads. My 300MM strong hemp fiber/type S mix is probably around 350 PSI compression, but it needs studs or it falls apart in a wall, roof, or floor. Out-of-plane shear/racking it helps a little, again, no studs it falls apart in high wind (90-150 mph)/seismic (CAT C+).
Unless someone has a ASTM or ICC certified manufacturer we could use to satisfy ASI 318 Ch 3? And a distributor that has low embodied energy to most locations?
I'm guessing Rome did not have the deicing chemicals we use on driveways, porches, roads today, and they had access to high strength geopolymers, and know how. How much concrete goes in the ground depends on wind/seismic/environmental loads/soils/mix/frost depth, and alot of other factors. Rome and most of the USA/world do not compare. That was then, this is now. Perhaps they had easy access to Silca Fume and were allowed higher levels to get their mechanical and physical properties up.
To take an analysis Engineering path a state licensed Architect would be involved to get a chemist and physicist hired to determine a design, mix to test, to get that info to a Structures Engineer (PE). Some ready mix companies have these groups of professionals but the cost to change the mix will be very expensive unless one can get a high volume of sales.
BTW here is a list of lime manufactures that ship to local lumber yards: https://lime.org/find-a-lime-plant/us-and-canadian-lime-companies/
Alot of the bigger ones like Carmeuse and Graymont are in that polluted mid-west where the diesel semis take off leaving high carbon foot prints behind. My guess is if you look at the total embodied energy it is higher than the OPC factory but I have not done the research. Most 3000 PSI structural slabs. walls, which is the bulk of 1-3 story homes in the USA only use OPC 1:3 aggregate, and due to pozzolans OPC is declining. Average cost $95/cu-yard/structural passes all ASTM code test.
SA offers USA hydraulic but VERY expensive, or ship from Europe, still low mechanicals 500-1500 for NHL 5, psi compression allowables: http://www.limes.us/
I'm going to try again and get some light burnt MGO and Silica Fume added to mine. Most have flyash, some slags, if one does not mind the heavy metals, and can air en-trained in freezing/thaw climates. Fibers are not allowed per IRC that will be another ACI R440 inspection battle unless you are in seismic Zone C or less like me then there is no reinforcement required which is not a good idea unless on top of undisturbed natural rock 4000-12,000 PSF. There is no code path for natural rock foundations, that will require the cost of a PE, definitely a full geotechnical report to the PE (unless you have one with experience/licensed in the building state), perhaps more testing, IF, you can get it by Architectural Control Committes (ACC) and/or Developers, flood insurance companies that may not understand, loan underwriters if applicable. I been in communications with all, not easy! They require a known code path, or stamped drawing if uncommon materials are used loan values go down (you need more down) insurance rates go up)..Builders may cut back thier warranties if it is experimental to them, trades will cost more and there may be learning curves, or some may have zero experience and quality will suffer. Trowls, floats, flat work, forms, may not work like they did on OPC concrete, some may dry faster or slower, need different admixes depending on weather, bracing, shoring, surface roughness/finishes/etching, cutting blades, sanding, grinding, can all vary, etc.... Bill or anyone if suggesting new concretes we also need installation guides, tooling, MSDS, etc...
Dale Hodgins wrote:Roman concrete was mentioned. The most famous artifact is the Pantheon. They didn't dump massive amounts into the ground.
From David Moore:
Unrecognized, the design of this ancient concrete building reveals unparalleled features not encountered in modern design standards. Recent studies reveal several major cracks in the dome, but it still functions unimpaired. This condition will surely excite the curiosity of our structural engineers. The building was built entirely without steel reinforcing rods to resist tensile cracking, so necessary in concrete members, and for this concrete dome with a long span to last centuries is incredible. Today, no engineer would dare build this structure without steel rods! Modern codes of engineering practice would not permit such mischief. No investor with knowledge of concrete design would provide the funding.
The Pantheon was built on marshy, unstable earth which gave a serious supporting problem to its builders. The Jutland Archaeological Society described in detail various aspects of the ring foundation; they found it rested on a bed of bluish colored river clay.8 This condition invited disaster, and in the final construction phase, the foundation cracked at the two ends of the North-South axis.9
As you can imagine, if one section of a building settles slightly faster and lower than an adjacent section, very large bending stresses are initiated at a point between these two sections which can crack the concrete. And uneven settling was the problem given to the builders. The present-day engineering solution to this type of foundation problem is to drive piles through the clay to bedrock so the building will be firmly supported all the way around. The Roman builders chose a different approach. They built a second ring to hold the first ring from cracking further and to give the clay more area to support the structure. It worked because the building has lasted over 1800 years.
In addition to keeping the crack from extending, the builders placed buttress walls on the south side opposite the massive porch. This acted as a clamping device; and although the structural projection appears to be an additional room, it only serves the purpose of being part of the clamp.
Initially, the width of this ring foundation was 23'-7" (7.2 m) wide, only about 3 feet (0.9 m) greater than the walls it supported. The second ring that binds the original together is 10 feet (3.0 m) wide making the total width of the foundation about 34 feet. From the floor level to the bottom of the foundation is 15'-4" (4.7 m).10
These rings are made of pozzolan concrete consisting of travertine pieces in layers held together by a mortar of lime and pozzolan. Interestingly enough, the Jutland Society's investigation showed the foundation material had become "rock hard," a case we might expect when we study the chemistry of pozzolanic reaction under these conditions.
I think the main take-aways here are; concrete can be made using lime as a cementitious binder, metal reinforcing is not needed(or desired) when good design is employed
and aggregates should be pozzolanic or carbonate rocks like travertine, marble, tufa, pumice etc.
Ann Torrence wrote:Why is it in my old SLC neighborhood, there were stretches of concrete sidewalk that were literally 100 years old and the newer stretches that were replacements for whatever reason degraded in less than 10 years?
Great question Ann!
There are a few reasons for this travesty:
1) Modern concrete has more cement in it than concrete poured 100 years ago since OPC was very expensive. Now if you buy a batch of ready-mix, they will try to sell you 6 bag which has as the name implies, 6 bags of OPC per cubic yard of concrete. This gives a very high early strength, but leaves too much of the cement as CH instead of converting it all to CSH. As I explained earlier, the CH migrates out of the concrete matrix, leaving a porous structure that allows water infiltration(along with chemicals like deicing chlorides and sulfates) and weakens the aggregate bond which results in cracking.
2) Thermal stress caused again by more OPC in the mix and a lack of a cooling/retarding agent. The chemical reaction is exothermic(creates heat) so if it is already hot outside and you have a "hot" mix, you get heat related cracking that gets worse with age.
3) Poor quality installation. The guys who pour sidewalks these days are not usually well trained, so quality control suffers.
4) This is still quality control; I see most sidewalks poured on a dry bedding, which sucks the water out of the mix too quickly and less CSH is produced, leaving more CH to cause problems.
If we are going to use energy intensive materials like OPC, we should at least understand them well enough to install the materials properly. Even so, don't expect your OPC concrete to last more than 200 years.
1. I do not have enough info (drawing’s, soil test, concrete composition and properties, climate zone, environmental loads, maintenance records, to draw ANY conclusions from the above. The Patheon write-up is very limited, the same for Ann’s question.
2. I hold that OPC is no less “green” than any other cement including lime, pozzolans, mgo, until I see a world-class cradle-to-grave embodied energy analysis by an independent non-profit source. This is not a matter of personal opinion or experience.
3. As far as what makes “modern concrete fail”, the same reason any concrete can fail, there are a ton of reasons. Besides what Bill wrote which I believe to be true, in part, not whole, here is a case of a 2010 KS dam rebuild project that shrinkage-cracked due to small aggregate was the culprit. The total OPC content of core samples were 588-lbs/yd3 compared to aggregates, water, ad-mixes… 3500 lbs/yd3, around 16% OPC. The issue was determined to be from absorptive aggregates not OPC. The solution was to add MGO (Premier admix). Today the Dam is doing well and more are being built in KS. I talked to civil engineer “client” involved.
Expansive soils/freeze/thaw a high plastic index cause lots of problems, or shrinkage, or the friction at the soil interface. That is one reason why the same mix can last for centuries and others will fail on the same sidewalk or lot. We know that too well in my area that is why our high index soils all require soil test now. If you soil test you can find large difference in shrink, plastic, and water indexes on the same lot, more so on the same road, bridge, side walk. When cracks occur for whatever reason, that opens the door for a lot of issues, including lime and earth construction that also react to salts and can develop effloresce. Sealers or renders are used to control the surface molecular structure, or, control vapor pressure permeability or liquid water intake. Surface with less than 2 nanometers are water barriers, 2-50 permeable but water resistance is what is desirable. Other noted issues are poor mixing, non-isotropic mixes, not achieving the proper air content, clumps and bulbs.
A person does not have to look far on the internet to see the MASSIVE amount of world-wide professionals, standards, specs, data, analysis, around OPC concrete and other systems. There is nothing in history we are missing that has not already been over analyzed, done, and redone MANY times. The biggest issues we have at the home level are people designing-building that should not be, or are not qualified.
If you read ACI-318 CH 5 there are provisions for “Alternative Concrete” mixes. You can create your own, have it tested to same specs that OPC is and look at the mechanical and physical properties, then take on the cost of liability, errors and omissions, cost of patents, etc. Not to worry hopefully these days if you fail they won’t put you to death.
I found out today limestone, lime (calcium carbonate) does not mix with Magnesium Oxy-chloride (MOC) (MAG board), so using a MOC plaster over it would be better than lime.