Sci­en­tists at the Kau­nas Univer­sity of Tech­nol­ogy (KTU), Lithua­nia, are de­vel­op­ing meth­ods for pro­duc­ing con­crete with­out ce­ment, us­ing in­dus­trial waste – fly ash. The fi­nal prod­uct is as strong as the tra­di­tional con­crete, is more re­silient to dam­ag­ing ef­fects of acid, and more sta­ble in cases of ex­po­sure to ex­treme heat and cold.

In order to pro­duce 1 met­ric ton of Port­land ce­ment, a ba­sic in­gre­di­ent of con­crete and most com­monly used type of ce­ment around the world, up to 1 ton of car­bon diox­ide (CO2) is re­leased. It is es­ti­mated that the global ce­ment in­dus­try is re­spon­si­ble for 7% of yearly car­bon diox­ide emis­sions into the at­mos­phere. Aim­ing to re­duce the neg­a­tive con­crete in­dus­try’s im­pact on the en­vi­ron­ment, KTU re­searchers have been in­ves­ti­gat­ing meth­ods of sub­sti­tut­ing Port­land ce­ment with other ma­te­ri­als.

Vy­tau­tas Bocullo, re­searcher at KTU Fac­ulty of Civil En­gi­neer­ing and Ar­chi­tec­ture, said: “At first, the idea that con­crete can be pro­duced with­out us­ing ce­ment seemed rad­i­cal. Now, af­ter sev­eral years of in­ten­sive work we suc­ceeded to de­velop al­kali ac­ti­vated con­crete, which com­pres­sive strength is 55 MPA (the same as in usual con­crete). In­stead of Port­land ce­ment we are us­ing al­kali ac­ti­vated in­dus­trial waste prod­ucts – fly ash, bio­fuel bot­tom ash, ALF3 pro­duc­tion waste – sil­icagel etc.”

Ac­cord­ing to the re­searcher, the big­gest ad­van­tage of this type of binder is that in its pro­duc­tion great amount of in­dus­trial waste, con­tain­ing ac­tive form of sil­i­con and alu­minium com­pounds can be used. The­o­ret­i­cally, any ma­te­rial con­tain­ing sil­i­con and alu­minium com­pounds could be used, such as blast fur­nace slag or metakaolin, ma­te­rial de­rived from mod­i­fi­ca­tion of clay min­eral kaoli­tine.

Treated with spe­cial al­ka­line so­lu­tion these ma­te­ri­als start melt­ing and bind­ing sim­i­larly to tra­di­tional ce­ment. De­pend­ing on the com­po­si­tion, the fi­nal prod­uct can be either geopoly­mer or al­kali-ac­ti­vated ma­te­rial. Al­kali ac­ti­vated con­crete is much more re­silient to the ef­fects of fire and acid. Also, due to its higher ph this con­crete is pro­tect­ing ar­ma­ture against cor­ro­sion.

Bocullo main­tains that al­kali ac­ti­vated con­crete can be used in­stead of tra­di­tional con­crete in many fields, and is be­com­ing a glob­ally pop­u­lar al­ter­na­tive to tra­di­tional con­crete. By prop­erly pre­par­ing raw ma­te­ri­als and the ac­ti­vat­ing so­lu­tion, such con­crete is so­lid­i­fy­ing in usual (+200) tem­per­a­ture. How­ever, in order to cost-ef­fi­ciently pro­duce this type of con­crete, it is rec­om­mended to use lo­cal ma­te­ri­als.

“We are try­ing to use waste ma­te­ri­als from lo­cal in­dus­try, such as alu­minium flu­o­ride pro­duc­tion waste – sil­ica gel and bio­fuel ash. The prepa­ra­tion of the sub­stance de­pends on the ma­te­rial it­self.

For ex­am­ple, fly ash of coal can be used in­stantly, but the bio­fuel ash need to be grinded up to the fine­ness of the ce­ment. In order to im­prove the qual­i­ties of the fi­nal prod­uct, sev­eral sub­stances can be mixed, but be­fore that their chem­i­cal com­po­si­tion and ad­di­tives need to be in­ves­ti­gated for their im­pact on the en­vi­ron­ment and on the com­pres­sive strength of the con­crete,” says Bocullo.

The re­search groups work­ing in the KTU Fac­ulty of Civil En­gi­neer­ing and Ar­chi­tec­ture are also ex­per­i­ment­ing and de­vel­op­ing other types of con­crete mix­tures, such as ul­tra-high per­for­mance con­crete, which is be­ing used for safe pro­duc­tion, self-re­new­ing con­crete and oth­ers.

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